Question 716005
I need help in finding quarterly interest. The question is: The bank guarantees to triple your money in 10 years if you open an account this month. The interest rate will be compounded quarterly. What is the quarterly interest rate?
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Formula for compound interest: A=P(1+i)^n, P=initial investment, i=interest per period, n=number of periods, A=amount after n-periods.
For given problem:
rewrite formula: A/P=(1+i)^n=3
n=10*4=40 quarterly periods
(1+i)^40=3
take log of both sides
40log(1+i)=log3
log(1+i)=log3/40≈.011928
convert to exponential form:
(1+i)=10^0.011928≈1.0278
i=1.0278-1≈.0278≈2.78% 
annual interest rate=4*2.78≈11.12%