There are some wafers in a box. The wafers can be put into plates of 4 or 12 with no wafers leftover. When the wafers are put into plates of 7, there are short of 1 wafers on the last plate. If there are more than 40 wafers but less than 60 wafers, how many wafers are there in the box?
If wafers can be put into plates of 4 or 12 with no wafers leftover, the number of wafers is a multiple of 12 as 12 is a multiple of 4.

Multiples of 12 that are greater than 40 but less than 60: 48, 60

Multiples of 7 that are greater than 40 but less than 60: 42, 49, 56
Multiples of 7 (- 1) that are greater than 40 but less than 60: 41, 48, 55

Common number = 48

Number of wafers = 48

Answer(s): 48