Gary works at Ghosts and Goblins, a Halloween store. He puts orange, black, and white Halloween candies in boxes. After he fills a box, 1/4 is orange, 1/6 is black, and 21 are white. How many candies does Boris put in each box?

Answer 1

1/4 +1/6 = 3/12 +2/12 = 5/12
12/12 - 5/12 = 7/12
so we finish filling 7/12 of the box with 21 white candles
if n is all the candles (7/12) n = 21
n = 12 * 21/7) = 12 * 3 = 36

Answer 2

3/12 + 2/12 = 5/12 amount in orange and black combined which leaves 7/12 as white
7/12 = 21/x : you know 21 is 7/12 of the total
x=36 : total number of candies