Question

What is the simple interest earned on $80 over 4 years at 9% interest?

Answer 1

Principle (P) = $ 80

Rate (R) = 9 %

Time (T) = 4 years

Simple Interest = $\frac{PRT}{100} = \frac{80*9*4}{100} = \frac{320*9}{100} = \frac{288}{10}$ = $ 28.8

Answer 2

Assuming interest is compounded once per year, we have
80(1+0.09)^4= around 112.9. After that, we subtract 80 from that to get around 32.9 dollars of interest over 4 years