Question

Tom has a $20 bill, a $10 bill, a $5 bill, and $1 bill. List the total costs possible for items he could buy if he receives no change.

Answer 1

$20, $25, $30, $21, $10, $15, $11, $5, $6, $1

Answer 2

using 1 bill: 1, 5, 10, 20
using 2 bills 6, 11 ,21 15, 25, 30
using 3 bills : 16, 26, 31, 35
using 4 bills : 36
For a total of 15 different costs

Notice Madison missed a few

Or

the number of subsets of 4 things
= 2^4 = 16
but that includes the null set , or not using any bills
so our answer = 2^4 - 1 = 15