Mixed practice · 21 problems

Choose the method.
Then do the math.

Work on paper first. For each question, draw the timeline, state the rate per period, choose the factor or criterion, and interpret the result. These original problems connect money, timing, and real decisions.

Paper-first mode gates hints and solutions until an answer is attempted. Use it to practice choosing a method independently before comparing your reasoning.

Answer unit: units

1. Find where costs and revenue meet

A product has fixed cost $22,000, price $12.50/unit, and variable cost $4.50/unit. Find break-even output.

Setup hint

Set revenue equal to total cost: pq = F + vq.

Open the visual solutionqBE=Fp−v=2200012.5−4.5=2750q_{BE}=\frac{F}{p-v}=\frac{22000}{12.5-4.5}=2750
  1. Set revenue equal to total cost: pq = F + vq.
  2. Contribution margin = $8.00 per unit.
  3. Divide fixed cost by margin; round UP only when output must be whole units.
0024.1k1.9k48.1k3.8kRevenue / cost ($)Quantity (units)
● Current scenarioRevenueCost · dashed
break-even quantity before whole-unit rounding · unitsqBE=Fp−v=2200012.5−4.5=2750q_{BE}=\frac{F}{p-v}=\frac{22000}{12.5-4.5}=2750

At least 2750 whole units are needed to cover costs. Break-even is not maximum profit.

Visual solution

Set revenue equal to total cost: pq = F + vq.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

2. Scale a plant without scaling every dollar

A known plant costs $600,000. Estimate a plant with 2.5 times capacity using b=0.65.

Setup hint

Use comparable technologies and price dates before scaling.

Open the visual solutionC2=C1(K2K1)b=600000(2.5)0.65=1088459.454413C_2=C_1\left(\frac{K_2}{K_1}\right)^b=600000(2.5)^{0.65}=1088459.454413
  1. Use comparable technologies and price dates before scaling.
  2. Capacity ratio = 2.5; exponent = 0.65.
  3. Multiply the known cost by ratioᵇ. A cost index adjusts date; the exponent adjusts size.
00.51.2M2.252.4M4Cost ($)Capacity ratio
● Current scenarioScaled costProportional benchmark · dashed
estimated new plant cost · $C2=C1(K2K1)b=600000(2.5)0.65=1088459.454413C_2=C_1\left(\frac{K_2}{K_1}\right)^b=600000(2.5)^{0.65}=1088459.454413

Cost rises less than proportionally with capacity: economies of scale in this range.

Visual solution

Use comparable technologies and price dates before scaling.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

3. Follow the loan balance

Borrow $18,000 at 6% effective annual interest for six end-of-year equal payments. Find the annual payment.

Setup hint

Choose the borrower viewpoint: loan receipt positive at time 0, repayments negative.

Open the visual solutionA=P(A/P,i,N)=3660.527313A=P(A/P,i,N)=3660.527313
  1. Choose the borrower viewpoint: loan receipt positive at time 0, repayments negative.
  2. Use one effective rate per payment period and payments at period end.
  3. Each payment = interest on opening balance + principal reduction; the last balance should be zero.
0123456Receipts (+)Expenses (−)

Period 0: +$18,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

YearOpening balance ($)Interest ($)Principal ($)Closing balance ($)
118,000.001,080.002,580.5315,419.47
215,419.47925.172,735.3612,684.11
312,684.11761.052,899.489,784.63
49,784.63587.083,073.456,711.18
56,711.18402.673,257.863,453.33
63,453.33207.203,453.330.00
level annual loan payment · $/yearA=P(A/P,i,N)=3660.527313A=P(A/P,i,N)=3660.527313

Total interest = NA − P = $3,963.16. A smaller payment with a longer loan can mean more total interest.

Visual solution

Choose the borrower viewpoint: loan receipt positive at time 0, repayments negative.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

4. Put a deferred annuity on the right date

Six benefits of $7,000 occur at years 5 through 10. At 8%, calculate their present worth at year 0.

Setup hint

Payments occur at years 5 through 10: 6 payments.

Open the visual solutionP0=A(P/A,i,N)(P/F,i,s−1)=23785.681912P_0=A(P/A,i,N)(P/F,i,s-1)=23785.681912
  1. Payments occur at years 5 through 10: 6 payments.
  2. At year 4, P = A(P/A,i,N) = $32,360.16.
  3. Discount that single local P through 4 periods to year 0.
012345678910Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

present worth at time 0 · $P0=A(P/A,i,N)(P/F,i,s−1)=23785.681912P_0=A(P/A,i,N)(P/F,i,s-1)=23785.681912

The annuity's local present date is year 4, not year 5.

Visual solution

Payments occur at years 5 through 10: 6 payments.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

5. Separate a base series from a gradient

A benefit starts at $2,000 in year 1 and rises by $300 each year for seven payments. At 6%, find present worth.

Setup hint

Separate the base uniform series from the arithmetic increments.

Open the visual solutionP=A(P/A,i,N)+G(P/G,i,N)=15799.671101P=A(P/A,i,N)+G(P/G,i,N)=15799.671101
  1. Separate the base uniform series from the arithmetic increments.
  2. Sum A/(1+i)^t plus (t−1)G/(1+i)^t for t = 1,…,N.
  3. At i = 0, P = NA + GN(N−1)/2. Equivalent annual gradient is G(A/G).
01234567Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

present worth of base plus gradient · $P=A(P/A,i,N)+G(P/G,i,N)=15799.671101P=A(P/A,i,N)+G(P/G,i,N)=15799.671101

The gradient starts with 0 at year 1, G at year 2, and (N−1)G at year N.

Visual solution

Separate the base uniform series from the arithmetic increments.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

6. Match interest to payment periods

A 12% nominal annual rate compounds monthly. Receive $1,000 at each quarter-end for four years. Find PW.

Setup hint

Convert nominal annual r into effective rate over one PAYMENT period.

Open the visual solutionip=(1+r/m)m/p−1=3.0301%,N=16,P=1000(P/A,ip,N)=12532.246293i_p=(1+r/m)^{m/p}-1=3.0301\%,\quad N=16,\quad P=1000(P/A,i_p,N)=12532.246293
  1. Convert nominal annual r into effective rate over one PAYMENT period.
  2. Number of payments N = years × payments/year = 16.
  3. Use i_p and N together. Never insert an annual rate beside a monthly N.
0246810121416Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

present worth of $1,000 at each payment-period end · $ip=(1+r/m)m/p−1=3.0301%,N=16,P=1000(P/A,ip,N)=12532.246293i_p=(1+r/m)^{m/p}-1=3.0301\%,\quad N=16,\quad P=1000(P/A,i_p,N)=12532.246293

$1,000 arrives at each payment-period end. If deposits occur between posting dates, this assumes fractional-period compounding; follow any stated bank convention.

Visual solution

Convert nominal annual r into effective rate over one PAYMENT period.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

7. Separate continuous interest from deposits

Deposit $1,500 at each half-year end for six years at an 8% continuous nominal annual rate. Find future worth.

Setup hint

The cash flows occur at deposit-period ends; this is not continuous cash inflow.

Open the visual solutionip=er/p−1,F=AerN−1er/p−1=22643.81457i_p=e^{r/p}-1,\quad F=A\frac{e^{rN}-1}{e^{r/p}-1}=22643.81457
  1. The cash flows occur at deposit-period ends; this is not continuous cash inflow.
  2. A payment period is 1/2 year; effective rate is e^(r/p)−1.
  3. Use a finite uniform series with 12 deposits. A single principal instead grows as Pe^(rN).
0123456789101112Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

future worth of discrete deposits · $ip=er/p−1,F=AerN−1er/p−1=22643.81457i_p=e^{r/p}-1,\quad F=A\frac{e^{rN}-1}{e^{r/p}-1}=22643.81457

Interest compounds continuously; the deposits remain discrete. At r=0 the limiting value is NA p = $18,000.00.

Visual solution

The cash flows occur at deposit-period ends; this is not continuous cash inflow.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

8. Make PW, FW, and AW tell the same story

Invest $36,000 now and receive $9,000 net annually for six years. At MARR 12%, find PW.

Setup hint

Draw the investment as negative at time 0 and net benefit as positive at years 1–N.

Open the visual solutionPW=1002.665912,FW=1979.084722,AW=243.874137PW=1002.665912,\quad FW=1979.084722,\quad AW=243.874137
  1. Draw the investment as negative at time 0 and net benefit as positive at years 1–N.
  2. PW = −I + A(P/A,i,N) = $1,002.67.
  3. FW = PW(F/P,i,N); AW = PW(A/P,i,N). Positive conversion factors preserve the sign and decision.
0123456Receipts (+)Expenses (−)

Period 0: −$36,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-19.6k0-790.122518.0k50Present worth ($)MARR (%)
● Current scenarioPresent worth
net present worth · $PW=1002.665912,FW=1979.084722,AW=243.874137PW=1002.665912,\quad FW=1979.084722,\quad AW=243.874137

The independent project meets the MARR on these assumed cash flows.

Visual solution

Draw the investment as negative at time 0 and net benefit as positive at years 1–N.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

9. Recover capital and cover operation

First cost is $18,000, salvage is 20% of first cost at year 6, operation costs $1,200/year, i=8%. Find EAC.

Setup hint

Capital recovery accounts for both the return OF capital and the required return ON capital.

Open the visual solutionCE=I−S(P/F)=15731.389343,CR=3402.941562,EAC=CR+E=4602.941562CE=I-S(P/F)=15731.389343,\quad CR=3402.941562,\quad EAC=CR+E=4602.941562
  1. Capital recovery accounts for both the return OF capital and the required return ON capital.
  2. Annualize the first cost and subtract annualized terminal salvage.
  3. Equivalent identity: CR=(I−S)(A/P)+Si. Add operating cost; a net-revenue AW would subtract this cost.
0123456Receipts (+)Expenses (−)

Period 0: −$18,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

equivalent annual cost including operation · $/yearCE=I−S(P/F)=15731.389343,CR=3402.941562,EAC=CR+E=4602.941562CE=I-S(P/F)=15731.389343,\quad CR=3402.941562,\quad EAC=CR+E=4602.941562

Salvage is $3,600.00 received at the end of year 6. EAC is a positive cost magnitude.

Visual solution

Capital recovery accounts for both the return OF capital and the required return ON capital.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Answer unit: %

10. Refine IRR in two interpolation steps

For −$50,000 now and +$15,000 annually for five years, start at 12% and 18%. Perform two interpolation steps and report the second rate estimate.

Setup hint

PW(12%) = $4,071.64 > 0; PW(18%) = $-3,092.43 < 0.

Open the visual solutioni1=15.410049%,PW(i1)=−202.007395,i2=15.248863%i_1=15.410049\%,\quad PW(i_1)=-202.007395,\quad i_2=15.248863\%
  1. PW(12%) = $4,071.64 > 0; PW(18%) = $-3,092.43 < 0.
  2. Interpolate i₁ = i_L + PW_L(i_H−i_L)/(PW_L−PW_H).
  3. Evaluate PW(i₁); retain the endpoints of opposite sign and interpolate again: 15.248863%.
012345Receipts (+)Expenses (−)

Period 0: −$50,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-24.0k0524.692525.0k50PW ($)Rate (%)
Present worth
second interpolated IRR estimate in percent · %i1=15.410049%,PW(i1)=−202.007395,i2=15.248863%i_1=15.410049\%,\quad PW(i_1)=-202.007395,\quad i_2=15.248863\%

Exact root 15.238237%. Replacing an endpoint based on the residual retains the sign-change bracket.

Visual solution

PW(12%) = $4,071.64 > 0; PW(18%) = $-3,092.43 < 0.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Answer unit: %

11. Make the external rate explicit

For −$10,000 now, +$6,000 at years 1 and 2, and −$5,000 at year 3, use external rate 10% and calculate ERR.

Setup hint

Separate positive and negative NET cash flows at each date.

Open the visual solutionPE=13756.574005,FR=13860,ERR=(FRPE)1/3−1=0.249984%P_E=13756.574005,\quad F_R=13860,\quad ERR=\left(\frac{F_R}{P_E}\right)^{1/3}-1=0.249984\%
  1. Separate positive and negative NET cash flows at each date.
  2. Discount all negatives to 0 at ε; accumulate positives to year 3 at ε.
  3. Bridge these two equivalent totals over 3 periods. ERR can be negative and changes with the external rate.
0123Receipts (+)Expenses (−)

Period 0: −$10,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

BucketEquivalent amount ($)
Outflows at 013,756.57
Inflows at 313,860.00
ERR in percent · %PE=13756.574005,FR=13860,ERR=(FRPE)1/3−1=0.249984%P_E=13756.574005,\quad F_R=13860,\quad ERR=\left(\frac{F_R}{P_E}\right)^{1/3}-1=0.249984\%

Under this convention, discount net negative cash flows and compound net positive cash flows using the stated external rate.

Visual solution

Separate positive and negative NET cash flows at each date.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Answer unit: %

12. Ask whether the extra investment earns its keep

Upgrading costs an additional $12,000 and saves an additional $3,000 per year for six years. Find incremental IRR and compare with MARR 9%.

Setup hint

Order alternatives by increasing initial investment and establish an acceptable defender.

Open the visual solutionΔCF=CFB−CFA,ΔIRR=12.978001%,ΔPW=1457.755771\Delta CF=CF_B-CF_A,\quad \Delta IRR=12.978001\%,\quad\Delta PW=1457.755771
  1. Order alternatives by increasing initial investment and establish an acceptable defender.
  2. Subtract A from B consistently at every date, including salvage.
  3. Solve incremental PW = 0; for this conventional increment ΔIRR ≥ MARR agrees with ΔPW ≥ 0. If the increment is nonconventional, use incremental PW.
0123456Receipts (+)Expenses (−)

Period 0: −$12,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-6.5k0-263.37256.0k50Incremental PW ($)Rate (%)
● Current scenarioPresent worth
incremental IRR in percent · %ΔCF=CFB−CFA,ΔIRR=12.978001%,ΔPW=1457.755771\Delta CF=CF_B-CF_A,\quad \Delta IRR=12.978001\%,\quad\Delta PW=1457.755771

The extra investment in B is justified relative to an acceptable A.

Visual solution

Order alternatives by increasing initial investment and establish an acceptable defender.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

13. Give unequal lives a fair comparison

Use A: $10,000, life 3, salvage $1,000, operating $2,200/year; B: $18,000, life 5, salvage $2,000, operating $900/year. At 8%, find EAC(B)−EAC(A).

Setup hint

Assume identical replacement cycles and continuing service. A costs $10,000 with $1,000 salvage; B costs $18,000 with $2,000 salvage.

Open the visual solutionEACA=5772.301626,EACB=5067.303273,ΔEAC=−704.998353EAC_A=5772.301626,\quad EAC_B=5067.303273,\quad \Delta EAC=-704.998353
  1. Assume identical replacement cycles and continuing service. A costs $10,000 with $1,000 salvage; B costs $18,000 with $2,000 salvage.
  2. Compute each cycle EAC at the same MARR, or repeat full cycles to 15 years and compare cost PW.
  3. For a fixed nonrepeatable study horizon, include terminal market values, replacements or service gaps explicitly. Never compare raw 3-year and 5-year PW as if horizons were equal.
AlternativeLifeEAC ($/year)15-year cost PW ($)
A35,772.3049,407.89
B55,067.3043,373.47
EAC(B) minus EAC(A) · $/yearEACA=5772.301626,EACB=5067.303273,ΔEAC=−704.998353EAC_A=5772.301626,\quad EAC_B=5067.303273,\quad \Delta EAC=-704.998353

Choose B for equal required service under repeatability. The common repeated study period is LCM(3,5)=15 years.

Visual solution

Assume identical replacement cycles and continuing service. A costs $10,000 with $1,000 salvage; B costs $18,000 with $2,000 salvage.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

14. Spot an ambiguous rate of return

Use flows −$1,000 at year 0, +$2,300 at year 1, −$1,300 at year 2. Find PW at 12%.

Setup hint

The sign pattern −,+,− permits multiple positive roots but does not guarantee them.

Open the visual solutionPW(i)=−1000+23001+i−1300(1+i)2,PW(12%)=17.219388PW(i)=-1000+\frac{2300}{1+i}-\frac{1300}{(1+i)^2},\quad PW(12\%)=17.219388
  1. The sign pattern −,+,− permits multiple positive roots but does not guarantee them.
  2. Multiply by (1+i)² and solve the resulting quadratic; the financial domain is i>−1.
  3. At cleanup cost $1,320, both 10% and 20% make PW zero. A single IRR ≥ MARR rule is unsafe.
012Receipts (+)Expenses (−)

Period 0: −$1,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-1.6k-50-791.372517.27100PW ($)Discount rate (%)
● Current scenarioPresent worth
present worth at MARR · $PW(i)=−1000+23001+i−1300(1+i)2,PW(12%)=17.219388PW(i)=-1000+\frac{2300}{1+i}-\frac{1300}{(1+i)^2},\quad PW(12\%)=17.219388

Admissible algebraic roots: 0.000%, 30.000%. Use PW at MARR to decide; multiple roots are ambiguous.

Visual solution

The sign pattern −,+,− permits multiple positive roots but does not guarantee them.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Money: enter dollars

15. Choose a feasible portfolio

Use a $26k budget and PW(B)=$11k in the displayed portfolio. A costs $10k with PW $7k; C costs $8k with PW $6k and requires A. Find the best feasible total PW.

Setup hint

Independent A and B may both be chosen if the budget permits.

Open the visual solutionmax⁡∑jPWjxj=18\max\sum_j PW_jx_j=18
  1. Independent A and B may both be chosen if the budget permits.
  2. Interdependency C ⇒ A imposes x_C ≤ x_A. Mutually exclusive alternatives would impose x_A+x_B≤1 instead.
  3. Enumerate feasible combinations and maximize total PW under the budget; highest standalone return is not enough.
PortfolioCost ($k)Total PW ($k)Feasible
None00Yes
A107Yes
B1511Yes
C (requires A)1813Yes
A+B2518Yes
A+B+C3324No
largest feasible portfolio present worth · $ thousandmax⁡∑jPWjxj=18\max\sum_j PW_jx_j=18

Best feasible portfolio: A+B. A costs 10 and yields PW 7; B costs 15; C costs 8 and adds PW 6 but requires A.

Visual solution

Independent A and B may both be chosen if the budget permits.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Review the setup and concept ↗
Combine the ideas

Combine patterns, timing, and decision rules.

Answer unit: years

16. Discount before measuring recovery

Spend $10,000 now and receive $3,000 at each of eight year-ends. At 10%, calculate interpolated discounted payback. State the integer recovery date if all receipts occur strictly at year-end.

Setup hint

Discount each of the eight receipts at 10%, then accumulate from the initial investment.

Open the visual solutionPBPd=(5−1)+490.4036611862.763969=4.263267PBP_d=(5-1)+\frac{490.403661}{1862.763969}=4.263267
  1. Discount each of the eight receipts at 10%, then accumulate from the initial investment.
  2. At year 4, $490.40 remains unrecovered. The next discounted receipt is $1,862.76.
  3. Interpolate 0.263267 of the next year; compare simple payback I/A = 3.333333 years. Neither method counts all value after recovery.
012345678Receipts (+)Expenses (−)

Period 0: −$10,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-10.0k02.0k414.0k8Cumulative recovery ($)Year
Undiscounted recoveryDiscounted recovery · dashed
interpolated discounted payback period · yearsPBPd=(5−1)+490.4036611862.763969=4.263267PBP_d=(5-1)+\frac{490.403661}{1862.763969}=4.263267

Recovery occurs within this eight-year life. Fractional recovery is an interpolation convention; strictly dated year-end receipts recover at the displayed integer year.

Visual solution

Discount each of the eight receipts at 10%, then accumulate from the initial investment.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Money: enter dollars

17. Save for a future capital purchase

A capital purchase needs $50,000 at year 10. At 8% effective annual interest, find equal end-of-year saving deposits for years 1 through 10.

Setup hint

The target F is at year 10, not time 0.

Open the visual solutionA=F(A/F,i,N)=3451.474435A=F(A/F,i,N)=3451.474435
  1. The target F is at year 10, not time 0.
  2. Use A/F, the sinking-fund factor. F/A would convert a given annual deposit to a future value.
  3. Each deposit earns interest until the target date; the last earns none before that date. The timeline is net saver cash flow, combining the last deposit with the target withdrawal.
012345678910Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

required annual sinking-fund deposit · $/yearA=F(A/F,i,N)=3451.474435A=F(A/F,i,N)=3451.474435

Equal saving deposits occur at years 1 through N. The target withdrawal is at year N, with the final deposit.

Visual solution

The target F is at year 10, not time 0.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Money: enter dollars

18. Finance withdrawals with an earlier saving series

Withdraw $7,000 at each year-end from year 4 through year 7. At 8%, what equal deposits at years 1, 2, and 3 exactly fund those withdrawals?

Setup hint

Four withdrawals of $7,000.00 start at year 4, so their local present date is year 3.

Open the visual solutionP0=W(P/A,i,4)(P/F,i,3)=18404.911504,A=P0(A/P,i,3)=7141.722487P_0=W(P/A,i,4)(P/F,i,3)=18404.911504,\quad A=P_0(A/P,i,3)=7141.722487
  1. Four withdrawals of $7,000.00 start at year 4, so their local present date is year 3.
  2. Discount the withdrawal present worth to year 0: $18,404.91.
  3. Three saving deposits must have the same PW, so A=P₀/(P/A,i,3). The diagram uses the saver viewpoint: deposits negative and withdrawals positive.
01234567Receipts (+)Expenses (−)

Period 0: +$0.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

required annual saving deposit · $/yearP0=W(P/A,i,4)(P/F,i,3)=18404.911504,A=P0(A/P,i,3)=7141.722487P_0=W(P/A,i,4)(P/F,i,3)=18404.911504,\quad A=P_0(A/P,i,3)=7141.722487

Deposits occur at years 1–3; withdrawals occur at years 4–7. Every cash flow is first valued at the same date.

Visual solution

Four withdrawals of $7,000.00 start at year 4, so their local present date is year 3.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Money: enter dollars

19. Value two benefit phases on one timeline

Invest $30,000 now. Receive $5,000/year at years 1–3 and $9,000/year at years 4–7. At MARR 10%, calculate net present worth.

Setup hint

The first three benefits form a series anchored at year 0.

Open the visual solutionPW=−30000+A(P/A,i,3)+B(P/A,i,4)(P/F,i,3)=3868.361395PW=-30000+A(P/A,i,3)+B(P/A,i,4)(P/F,i,3)=3868.361395
  1. The first three benefits form a series anchored at year 0.
  2. The four later benefits form a different series anchored at year 3.
  3. Discount that second series by three years, then combine both with the negative initial investment.
01234567Receipts (+)Expenses (−)

Period 0: −$30,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

net present worth of the two-stage project · $PW=−30000+A(P/A,i,3)+B(P/A,i,4)(P/F,i,3)=3868.361395PW=-30000+A(P/A,i,3)+B(P/A,i,4)(P/F,i,3)=3868.361395

This two-stage independent project meets MARR.

Visual solution

The first three benefits form a series anchored at year 0.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Money: enter dollars

20. Compare machines on a fixed service horizon

Service is required for four years. A costs $10,000 and $2,000/year, with year-4 market value $4,000. B costs $18,000 and $1,000/year, with year-4 market value $8,000. At 8%, compute positive cost PW(B) minus cost PW(A).

Setup hint

A costs $10,000 and $2,000/year; B costs $18,000 and $1,000/year. Both provide required service through year 4.

Open the visual solutionPWC,A=13684.134269,PWC,B=15431.888018,ΔPWC=1747.753749PW_{C,A}=13684.134269,\quad PW_{C,B}=15431.888018,\quad\Delta PW_C=1747.753749
  1. A costs $10,000 and $2,000/year; B costs $18,000 and $1,000/year. Both provide required service through year 4.
  2. Use their given year-4 market values, not salvage from their natural useful lives.
  3. Compute positive cost PW = purchase + operating PW − terminal-value PW; compare B minus A and choose the smaller cost.
Alternative4-year cost PW ($)
A13,684.13
B15,431.89
4-year cost PW(B) minus cost PW(A) · $PWC,A=13684.134269,PWC,B=15431.888018,ΔPWC=1747.753749PW_{C,A}=13684.134269,\quad PW_{C,B}=15431.888018,\quad\Delta PW_C=1747.753749

Required service ends at year 4. Choose A on this common cost basis; no repeated-cycle assumption is needed.

Visual solution

A costs $10,000 and $2,000/year; B costs $18,000 and $1,000/year. Both provide required service through year 4.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Money: enter dollars

21. Evaluate a growing-benefit investment

Invest $10,000 now. Eight year-end benefits start at $2,000 and grow 4% per year. At MARR 10%, find net PW.

Setup hint

There are eight benefits, with A₁ at year 1 and A₁(1+g)⁷ at year 8.

Open the visual solutionPW=−10000+∑t=18A1(1+g)t−1(1+i)t=2051.747922PW=-10000+\sum_{t=1}^8\frac{A_1(1+g)^{t-1}}{(1+i)^t}=2051.747922
  1. There are eight benefits, with A₁ at year 1 and A₁(1+g)⁷ at year 8.
  2. Use the geometric-series PW (or direct discounted summation); handle g=i by its limit.
  3. Subtract the $10,000 initial investment and interpret the sign at MARR.
012345678Receipts (+)Expenses (−)

Period 0: −$10,000.00. This is the time-zero cash flow. Periods use the payment interval stated in the model.

-5.9k01.3k258.4k50Project PW ($)MARR (%)
● Current scenarioPresent worth
net present worth of the growing-benefit project · $PW=−10000+∑t=18A1(1+g)t−1(1+i)t=2051.747922PW=-10000+\sum_{t=1}^8\frac{A_1(1+g)^{t-1}}{(1+i)^t}=2051.747922

The growing-benefit investment meets MARR.

Visual solution

There are eight benefits, with A₁ at year 1 and A₁(1+g)⁷ at year 8.

Cash-flow dates and signs are part of the answer. Model values retain precision; displays round money to cents. Illustrative assumptions exclude taxes and inflation unless stated.

Checks allow 0.1% numerical rounding (minimum $0.05 or 0.001 in the stated nonmonetary unit). Interpolated factors and rates are approximations; keep table precision consistent.

Diagnose the error before repeating.

For each missed question, identify whether the issue was viewpoint, timing, rate conversion, factor selection, algebra, or the decision rule. Then change the relevant control and explain why the answer moves. Topic pages include another numerical scenario and a conceptual check.