SOLUTION: An investment of $25,400 is placed into an account that earns 6.5% interest compounded quarterly. In how many years will the investment be worth twice the original amount?

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: An investment of $25,400 is placed into an account that earns 6.5% interest compounded quarterly. In how many years will the investment be worth twice the original amount?       Log On


   



Question 165019This question is from textbook
:
An investment of $25,400 is placed into an account that earns 6.5% interest compounded quarterly. In how many years will the investment be worth twice the original amount?
I am thinking I would use the compound interest formula A = P(l + i)^n
I had set it up like below but I seem I am doing it wrong. Should I have went with 4 or 12? any help appreciated
i = 6.5%/4 = .065/4 = .01625
101600 = 25,400(1 + .01625)^n
101600 = 25400(1.01625)^n
4 = (1.01625)^n
log4 = log(1.01625)^n
log4 = n log 1.01625
log4/log1.01625 = n
86.0017 = n
86.0017/4 = 21.50004
In approx. 21.5 years , the investment will be worth $101,600.
This question is from textbook

Answer by jojo14344(1513) About Me  (Show Source):
You can put this solution on YOUR website!

I dont know how you got your answer, but try this one:
Use compound interest formula --> A=P%281%2B%28i%2Fm%29%29%5E%28mn%29
where,
P=initial_investment=25400
A=Future_amount=50800, wants twice the initial invest. right?
i=interest
n=years
m=number_of_times_compunded
Continuing,
50800=25400%281%2B%280.065%2F4%29%29%5E%284n%29
50800=25400%281%2B0.01625%29%5E%284n%29
50800%2F25400=%281.01625%29%5E%284n%29
2=%281.01625%29%5E%284n%29
log2=%284n%29log1.01625
log2%2Flog1.01625=4n
43=4n -----> cross%2843%2910.75%2Fcross%284%29=cross%284%29n%2Fcross%284%29
n=10.75years ---> 10years & 9 months, ANSWER
Let's check, using our formula,
A=P%281%2B%28i%2Fm%29%29%5E%28mn%29
50800=25400%281%2B%280.065%2F4%29%29%5E%284%2A10.75%29
50800=25400%281%2B0.01625%29%5E%2843%29
50800=25400%281.01625%29%5E%2843%29
50800=25400%282%29
50800=50800
Thank you,
Jojo