Answer:
about 1.33% per month
Step-by-step explanation:
The future value is given by ...
FV = P(1 +r)^n
where P is the principal, r is the monthly interest rate, and n is the number of months. Solving for r, we get ...
FV/P = (1 +r)^n . . . . . . . divide by P
(FV/P)^(1/n) = 1 +r . . . . . take the n-th root
r = (FV/P)^(1/n) -1 . . . . . subtract 1
Filling in the given numbers, we have ...
r = (8140/4320)^(1/48) -1 ≈ 0.013286 ≈ 1.33%
The rate of interest per month is about 1.33%.
