If i deposit money today in an account that pays 6.5% annual interest, how long will it take to double.
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Compound interest formula: A=P(1+i)^n, P=initial investment, i=interest rate per period, A=amount after n periods.
A/P=(1+i)^n
For given problem:
n=periods(years)
A/P=2, i=.065
(1+.065)^n=2
1.065^n=2
take log of both sides
nlog(1.065)=log(2)
n=log(2)/log(1.065)
n≈11 yrs
ans: It will take 11 years to double the deposit money