Question

A student makes a $10.25 purchase at the bookstore with a $20 bill. The store has no bills and gives change in quarters and fifty cent pieces. There are 30 coins in all. How many of each kind are there?

Answer 1

20-10.25=9.75 in change
There are different ways to solve this. Here's one way:
Let x = number of quarters in the change
0.25x+0.5(30-x)=9.75
x = 21
So 21 quarters and 9 fifty-cent coins.