Question

A family member has some five dollar bills and one dollar bills in their wallet. Altogether she has 18 bills and a total of $62. How many bills does she have?

Answer 1

X - the number of five dollar bills
y - the number of one dollar bills

She has 18 bills in total.
$x+y=18 \\ y=18-x$

She has $62.
$5x+y=62 \\ y=62-5x$

Set both expressions equal to each other:
$18-x=62-5x \\ -x+5x=62-18 \\ 4x=44 \\ x=11 \\ \\ y=18-x=18-11=7$

She has 11 five dollar bills and 7 one dollar bills.