SOLUTION: Use the compound interest equation {{{A= P(1 + r/n)^nt}}} to find how long, to the nearest tenth of a year, it will take a $5000 investment to double if it is invested at 7% intere

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Question 38110: Use the compound interest equation to find how long, to the nearest tenth of a year, it will take a $5000 investment to double if it is invested at 7% interest compounded quarterly. The answer is 10.0 years, I just can't figure out how to get it.
Found 2 solutions by fractalier, josmiceli:
Answer by fractalier(6550) (Show Source):
You can put this solution on YOUR website!
Okay, from the equation
A = P(1 + r/n)^nt
we plug in what we know and solve for what we don't know...
10000 = 5000(1 + (.07/4))^4t
now divide by 5000
2 = (1 + (.07/4))^4t
take the log of both sides
log 2 = 4t*log(1 + (.07/4))
now solve for t...
t = log 2 / 4(log 1.0175)
t = 9.988 years or roughly 10 years

Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
I do get 10 years

I'm assuming that, if t is in years, n means number of times
per year that the interest is compounded.
10000 is what you end up with (double the 5000)

divide both sides by 5000

take the log of both sides. Remember that log(a^b) = b*log(a).