Question

Three eights of the cast in a musical have to sing. What fraction of the cast does not have to sing

Answer 1

5/8 of the cast does not have to sing. You find this by doing 8/8 - 5/8

Answer 2

3/8 has to sing
8/8 is all
all=haveto+don'thaveto
all=8/8
haveto=3/8
subsitute
8/8=3/8+don'thaveto
subtract 3/8 from both sides
8/8-3/8=5/8
5/8=don'thavetosing

answer is 5/8