Answer: 56
Explanation:
Let the number of $5 be x
Let the number of $2 be y.
Based on the information given, we can form an equation as:
x + y = 128 ........ i
5x + 2y = 424 ....... ii
Multiply equation i by 2
Multiply equation ii by 1
2x + 2y = 256 ...... iii
5x + 2y = 424 ....... iv
Subtract iii from iv
3x = 168
x = 168/3
x = 56.
Therefore, there were 56 $5 bills.