3 7/8-1 1/2 change mixed numbers to improper fractions
rule a b/c=(ac+b)/c
31/8-3/2 make a common denominator of 8
31/8-(3/2)(4/4)
31/8-12/8
(31-12)/8
19/8 convert back to a mixed number
(16+3)/8
2+3/8
2 3/8
I know that there is easier ways to do this but this is the way to do it when it isn't an easy problem :P
