Does this work? 
Sally took a 50 dollars bill with her going to the laundromat, and after she came home she looked through he pockets and she had: 
2x 20 dollar bill
1x 5 dollar bill
1x 1 dollar bill. 
how many loads of laundry did she do? 
answer: she has left: 2*20+5+1=46 dollars
before she had 50 dollars, so she must have spent 50-46=4 dollars, which is 2*2, so she did two loads!