Question

Caitlyn needs to mail a USB drive to a friend. She uses 45-cent stamps and 7-cent stamps to pay $1.91 in postage. How many of each stamp did Caitlyn use?

Answer 1

191 = 7* 27 + 2
191 = 4* 45 + 11
191 = 3* 45 + 56
181 = 3*45 + 8*7

So Caitlin used 3 45-cent stamps and 8 7-cent stamps.