Chris invests $10 000 at 7.2%/a compounded monthly. How long will it take for his investment to grow to $25 000?

Answer 1

7.2 % per annum, compounded monthly corresponds to a rate of .072/12 or .006 per month

so we have:
10000(1.006)^n = 25000 , where n is the number of months
1.006^n = 2.5
take log of both sides

log (1.006)^n = log 2.5
n log 1.006 = log 2.5
n = log 2.5/log1.006 = appr 153 months