Felicia put $175 into a CD that pays 4% interest, compounded semiannually. According to the rule of 72, approximately how long will it take for her money to double?
The compound interest is given by: A=p(1+r/100)^n where; A=amount p=principle r=rate n=time therefore the time taken for Felicia's money to double will be: 350=175(1+4/100)^n 350/175=1.04^n 2=1.04^n therefore introducing natural longs we get: ln2=nln1.04 n=(ln2)/(ln1.04) n=17.7 years The answer is 17.7 years
