Money Problem Involving Fives and Tens

A man has $185 in five and ten dollar bills.  How many of each did he has if he had 7 more fives than tens?

x = number of ten dollar bills
x + 7 = number of five dollar bills   {he has 7 more fives than tens} 

10x + 5(x + 7) = 185   {value of bill times number of bills equals total value}
10x + 5x + 35 = 185   {used distributive property}
15x + 35 = 185   {combined like terms}
15x = 150   {subtracted 35 from each side}
x = 10   {divided each side by 15}
x + 7 = 17   {substituted 10, in for x, into x + 7} 

10 ten dollar bills
17 five dollar bills

- Algebra House