Math
posted by Annie .
George invests $ 15 000 at 7.2%/a compounded monthly . How long will it take for his investment to grow to $ 34 000

let the number of months be n
i = .072/12 = .006
15000(1.006)^n = 34000
1.006^n = 2.266666...
log 1.006^n = log 2.66666..
n log 1.006 = log 2.26666...
n = log 2.266666.../log 1.006
= 136.79 or 137 months
= 11 years and 5 months