Calvin has 13 coins , all of which are quarters and nickels. The coins are worth $2.45. How many of each coin does Calvin have ?
q=quarters
n=nickles
q+n=13
.25q+.05n=2.45 (multiply by 100)
25q+5n=245
n=-q+13
25q+5(-q+13)=245 (Substition)
25q-5q+65=245
20q+65=245 (Substract 65 from both sides)
20q=180
q=9
9+n=13
n=4
To check
.25(9)+.05(4)=2.45