There are some wafers in a box. The wafers can be put into plates of 5 or 15 with no wafers leftover. When the wafers are put into plates of 8, there are short of 4 wafers on the last plate. If there are more than 50 wafers but less than 70 wafers, how many wafers are there in the box?
If wafers can be put into plates of 5 or 15 with no wafers leftover, the number of wafers is a multiple of 15 as 15 is a multiple of 5.

Multiples of 15 that are greater than 50 but less than 70: 60

Multiples of 8 that are greater than 50 but less than 70: 56, 64
Multiples of 8 (- 4) that are greater than 50 but less than 70: 52, 60

Common number = 60

Number of wafers = 60

Answer(s): 60