x - the number of five dollar bills
y - the number of one dollar bills
She has 18 bills in total.
[tex]x+y=18 \\ y=18-x[/tex]
She has $62.
[tex]5x+y=62 \\
y=62-5x[/tex]
Set both expressions equal to each other:
[tex]18-x=62-5x \\
-x+5x=62-18 \\
4x=44 \\
x=11 \\ \\ y=18-x=18-11=7[/tex]
She has 11 five dollar bills and 7 one dollar bills.
