Of the 216 students on the playground three-eighths are wearing white shoes how many children on the playground are not wearing white shoes

If 3/8 ARE wearing white schoes
Then 5/8 AREN'T wearing white shoes 
because

8/8 - 3/8 = 5/8
8/8 is the same as 1

Therefore, 
5/8 x 216/1 = y
If this is mental maths then,

You can cancel the 216 by 8 because the denominator of 5/8 is 8 to make 27

Therefore, the answer is 135

First, you need to turn 3/8 in to a decimal. You can do that by dividing 3 by 8. You should get .375 now multiply that with 216. you should get 81. That means 81 kids are wearing white shoes. To find how many are not wearing white shoe, subtract 81 from 216. That gives you 135. 135 students are not wearing white shoes.