interest compounded monthly

Question

If Kevin invests $50,000 into an account that earns 6.15% interest compounded monthly, how long will it take his money to double? (round to one decimal place)

A.135.6 years

B.11.6 years

C.11.3 years

D..9 years

Answer 1

Use the compound interest formula,

A= P(1+r/n)^nt

Plugging in our values,

100000=50000(1+.0615/12)^12t

where t or the number of years is what we are trying to find.

2=(1.005125)^12t

log (2) = 12t log (1.005125)

solving for t we get 11.3 years. So C is the answer