Question 61059
n = number of $5's
m = number of $10's
n + m = 12
5n + 10m = 100
5n + 10(12 - n) = 100
5n + 120 - 10n = 100
5n = 20
n = 4
m = 12 - n
m = 8
check
5*4 + 10*8 = 100
20 + 80 = 100
OK