Question

How might simple interest be described as a problem

Answer 1

i guess simple interest means you are adding the same amount each time, not compounding. so for example if you have $100 and you earn 5% simple interest each year you make another $5 so the numbers look like
100
105
110
115
120
etc,
same as an arithmetic series with a = 100 and d = 5

Answer 2

Satellite's right :)))