# Some $10 bills and some $20 bills are in a shoe box for a total of 52 bills. The total amount is $680. How many bills are $20?

##### 1 Answer

Jul 15, 2016

There are sixteen $20 bills.

#### Explanation:

Denote number of $10 bills as x and number of $20 bills as y.

The situation becomes

with

We now have a pair of simultaneous equations which is easy to solve. We multiply the second by 10, yielding:

and subtract it from the first, leaving:

substitution into either equation then produces that