Question

How many pairs of whole numbers numbers have a sum of 40

Answer 1

 there are 20
1.       1 + 39 = 40
2.       2 + 38 = 40
3.       3 + 37 = 40
4.       4 + 36 = 40
5.       5 + 35 = 40
6.       6 + 34 = 40
7.       7 + 33 = 40
8.       8 + 32 = 40
9.       9 + 31 = 40
and the list goes on and on