Question
A $5000 investment earns 7.2% annual interest, and an $8000 investment earns 5.4%, both compounded annually. How long will it take for the smaller investment to catch up to the larger one?
Answers
Use the compound interest formula:
A=P(1+i)^n
A=accumulated amount after n periods (years)
P=principal
i=interest per compounding period
n=number of compounding periods
If the smaller investment catches up to the larger one, then the accumulated amounts would be equal. Therefore by equating the two, we get an equation in which the only unknown is n, the number of periods (years in this case).
5000(1.072)^n=8000(1.054)^n
Solve for n:
(1.072/1.054)^n = 8000/5000
take logs and apply laws of logarithm,
n*log(1.072/1.054) = log(8000/5000)
n=log(8000/5000)/log(1.072/1.054)
I get approximately n=28.
Substitute in above solution to get the exact value.
A=P(1+i)^n
A=accumulated amount after n periods (years)
P=principal
i=interest per compounding period
n=number of compounding periods
If the smaller investment catches up to the larger one, then the accumulated amounts would be equal. Therefore by equating the two, we get an equation in which the only unknown is n, the number of periods (years in this case).
5000(1.072)^n=8000(1.054)^n
Solve for n:
(1.072/1.054)^n = 8000/5000
take logs and apply laws of logarithm,
n*log(1.072/1.054) = log(8000/5000)
n=log(8000/5000)/log(1.072/1.054)
I get approximately n=28.
Substitute in above solution to get the exact value.
Related Questions
An investment initially worth $5300 earns 7.7% annual interest, and an investment initially worth $8...
Two investments in high- technology companies total $1,100. If one investment earns 10% annual inter...
Suppose that an investment pf 8000 earns interest at a rate of 15% compounded per year. How much int...
4. You invest $2000 in an investment that earns 6% interest, compounded quarterly. How much will the...