Answer:
(A) payback in 3.42 years
(B) It doesn't payback in six years. payback is 6.66 years
Step-by-step explanation:
(A) because discount rate is zero we are doing the payback period
![(investment)/(cashflow \: per \: year) = payback \: in \: years](https://img.qammunity.org/2020/formulas/business/college/mevm52lexa2fhna605kd1qpdkklgl32gio.png)
10000 investment / 2920 per year = 3.4246
(B) here there is a discount rate so we need to solve ussing the annuity formula for the time which makes the 2,920 cash flow equal to 10,000
![annuity * \frac{1 - {1 + rate}^( - time) }{rate} = principal](https://img.qammunity.org/2020/formulas/business/college/kald72p0k53uq4t53c0uyfhmwi7k0wxzm8.png)
we post our givens in the formula
![](https://img.qammunity.org/2020/formulas/mathematics/high-school/2s1zskintisw2ersplikedmrk39aeu01.png)
we pass the annuity and rate to the second part of the equation
![1 - {1.21}^( - time) = 10000 \: / 290 * .21](https://img.qammunity.org/2020/formulas/business/college/jfsclk2mdewqrz4dlis5nqpgn05i40di2l.png)
10,000/2920*0.21= 0.7191...
for rounding porpuses I will refer to this as "a"
This means you have to work with the complete number, don't round it.
then, we work the equation a little more to reach this structure
![{1.21}^( - time) = 1 - a](https://img.qammunity.org/2020/formulas/business/college/1vsdgctwu5kbm7j6tidu69fxik8h53ss2m.png)
finally, we use log properties to solve for time
![(log (1 - a))/( log(1.21) ) = - 6.662638](https://img.qammunity.org/2020/formulas/business/college/ml5axa6xbw917m790kcrdon8zykxisqv7q.png)
-time = -6.662638
time = 6.662638
But the project life is six years... so the project doesn't payback at this discount rate.