three eighths
Instead of "a half", write "eight sixteenths". That doesn't change the value of any numbers, but it makes it a lot easier to subtract the three sixteenths from the eight sixteenths.
One and three quarters
20
Seven and a half (:
It is minus one half.
Seven to eight and a half inches in length.
It is: 7/8-1/2 = 3/8
seven eighths
Three pounds, eight ounces.
81/2 − 7/8 = 75/8
Eight and seven eighths.