Math 103
Simple and Compound Interest
Practice Problems with answers
1. If $3,000 is loaned for 4 months at a 4.5% annual rate, how much interest is earned? $45
2. A loan of $4,000 was repaid at the end of 10 months with a check for $4,270. What annual rate
of interest was charged? 8.1%
3. A newborn child receives a $20,000 gift toward a college education from her grandparents.
How much will the $20,000 be worth in 17 years if it is invested at 7% compounded quarterly?
$65, 068.44
4. What will a $210,000 house cost 10 years from now if the inflation rate over that period averages
%3 compounded annually? $282, 222.44
5. Which is a better investment: 9% compounded monthly or 9.3% compounded annually? 9%
monthly
6. If an investment company pays 6% compounded semiannually, how much should you deposit
now to have $10,000 5 years from now? $7, 440.94
7. If an investment company pays 9% compounded continuously, how much should you deposit
now to have $25,000 9 years from now? $11, 121.45
8. How long will it take $4,000 to grow to $9,000 if it is invested at 7% compounded monthly?
11.62 years, or 11 years and 8 months
9. How long will it take $6,000 to grow to $8,600 if it is invested at 9.6% compounded continuously?
3.75 years
10. How long will it take money to double if it is invested at
(a) 10% compounded quarterly? 7.02 years, which rounds up to 7 years and 3 months (1
quarter)
(b) 10% compounded continuously? 6.93 years