Solution: If there are N stamps then 36<= N <= 48
Furthermore if F, C and W denote the numbers given to each child (respectively) then F = (3/2)C and W = (F + C )/2
Written in terms of C we have W = (5/4) C.
Adding we get N = (3/2)C + (5/4)C + C = (15/4)C
Hence we have C = 4N/15 and C is integer!
We deduce that N is divisible by 15, so N must equal 45.
Therefore C = 4x45/15 = 12
It follows that F = 18 (half as much again)
and W = 15 (half of 12 plus 18)
Check: 12 + 18 + 15 = 45 (OK)