Question

Every morning Jenna empties her pockets and puts her change in a jar. At the end of the week she counts her money. One week she had 40 coins, all of them dimes and quarters. When she added them up, she had a total of $7.75. l

Let d = number of dimes and
q = number of quarters

How many dimes did jenna have ?

Answer 1

If all of her coins were quarters, she would have $10.00. She has 2.25 less than that. Each dime that replaces a quarter reduces the total by 0.15, so she must have 2.25/0.15 = 15 dimes.