Question 1100225
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<pre>
As they just explained to you, the formula for the growing amount (Future Value of the Account) is


A = {{{P*(1+r)^n}}} = {{{80000*(1+0.2)^n}}} = {{{80000*1.2^n}}}.


And they want you to find n, when A becomes doubled 80000, i.e.

160000 = {{{80000*1.2^n}}}.


Divide both sides by 80000. You will get

2 = {{{1.2^n}}}  ====>  {{{log((2))}}} = {{{log(((1.2)^n))}}} = {{{n*log((1.2))}}}.


============>  n = {{{log((2))/log((1.2))}}} = {{{log((2))/0.079181}}} = 3.8 years.


<U>Answer</U>.  It will happen after 4 years.
</pre>

After 4 years happy Bill will have more than doubled amount at his account:  &nbsp;&nbsp;{{{1.2^4}}} = 2.0736.