Eileen saves dimes and quarters. She has 40 coins, which total $6.55, in her bank. How many of each coin does she have?
Let x be the number of dimes
Then 40 - x = the number of quarters
So
number of dimes * value each + number of quarters * value each = total value
x * .10 + (40 - x) * .25 = 6.55 simplify
.10x + 40 * .25 - .25x = 6.55
.10x - 10 - .25x = 6.55
-.15x = 6.55 -10
-.15x = -3.45 divide both sides by -.15
x = 23 =number of dimes
40 - 23 = 17 = number of quarters