# SIMPLE AND COMPOUND INTEREST

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SIMPLE AND COMPOUND INTEREST
Since this section involves what can happen to your money, it should be of INTEREST to you!

I = PRT 100 IMPLE INTEREST FORMULA Annual interest rate Interest paid
Time (in years) 100 Principal (Amount of money invested or borrowed)

If you invested \$ in an account that paid simple interest, find how long you’d need to leave it in at 4% interest to make \$10.00. enter in formula as a decimal I = PRT 100 10 = (200)(0.04)T 1.25 yrs = T Typically interest is NOT simple interest but is paid semi-annually (twice a year), quarterly (4 times per year), monthly (12 times per year), or even daily (365 times per year).

COMPOUND INTEREST FORMULA
annual interest rate (as a decimal) Principal (amount at start) time (in years) amount at the end number of times per year that interest in compounded

Find the amount that results from \$500 invested at 8% compounded quarterly after a period of 2 years. 4 (2) .08 500 4 Effective rate of interest is the equivalent annual simple rate of interest that would yield the same amount as that made compounding. This is found by finding the interest made when compounded and subbing that in the simple interest formula and solving for rate. Find the effective rate of interest for the problem above. The interest made was \$ Use the simple interest formula and solve for r to get the effective rate of interest. I = Prt =(500)r(2) r = = 8.583%

Acknowledgement I wish to thank Shawna Haider from Salt Lake Community College, Utah USA for her hard work in creating this PowerPoint. Shawna has kindly given permission for this resource to be downloaded from and for it to be modified to suit the Western Australian Mathematics Curriculum. Stephen Corcoran Head of Mathematics St Stephen’s School – Carramar