9514 1404 393
Answer:
C) 12y 8m
Step-by-step explanation:
The amount of principal P at compound monthly at interest rate r per year is given by ...
A = P(1 +r/12)^(12t) . . . . after t years
Here, we want to find t, so ...
A/P = (1 +r/12)^(12t)
log(A/P) = (12t)·log(1 +r/12)
t = log(A/P)/(12·log(1 +r/12))
Filling in the given values, we find t to be ...
t = log(8000/4000)/(12·log(1 +0.055/12)) ≈ 12.6315 ≈ 12 years 7.6 months
It will take about 12 years 8 months to double the money.