Question
At what interest rate (compounded monthly) should you invest if you would like to grow $3,633.07 to $4,126.00 in 81 months?
Answers
oobleck
3633.07 (1 + r/12)^81 = 4126
(1 + r/12)^81 = 1.135
81 log(1 + r/12) = log 1.135
log(1 + r/12) = 0.000682
1 + r/12 = 10^0.000682 = 1.00157198
r/12 = 0.00157198
r = 0.01886 = 1.89%
(1 + r/12)^81 = 1.135
81 log(1 + r/12) = log 1.135
log(1 + r/12) = 0.000682
1 + r/12 = 10^0.000682 = 1.00157198
r/12 = 0.00157198
r = 0.01886 = 1.89%