Question

Denise put $95 into a cd that pays 5.2% interest compounded monthly. according to the rule of 72, approximately how long will it take for her money to double? round your answer to the nearest tenth.

Answer 1

72/5.2=13.8years ......................

Answer 2

It will take 13.67 months for her money to double

Explanation:

We are given

Denise put $95 a cd

so, P=95

that pays 5.2% interest compounded monthly

so, r=0.052

We are given

Her money gets doubled

so, A=2*95=190

now, we can use formula

`A=P(1+r)^t`

where

t is time in months

we can plug values

`190=95(1+0.052)^t`

`2=(1.052)^t`

now, we can solve for t

`\ln \left(2\right)=\ln \left(1.052^t\right)`

`t=(\ln \left(2\right))/(\ln \left(1.052\right))`

`t=13.67`