Question

Armando put $78 into a CD that pays 4.9% interest compounded monthly. According to the Rule of 72, approximately how long will it take for his money to double? A.15.9 years B.14.7 years C.146.9 years D.159.2 years

Answer 1

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Answer 2

double of money is 78*2 = 156
then:
156 = 78*(1+0.049/12)^n
we need to find n:
156/78 = (1+0.049/12)^n
using Log:
Log(2) = n*Log(1+0.049/12)
Log(2)/Log(1+0.049/12) = n
then:
n= 170 months

Answer 3

B 14.7 ?

Answer 4

14.17
You must have a typing error.

Answer 5

time = 170 months/12 months per year = 14.17

Answer 6

14.7 years