Listing each pair could be one way to work this out
1 + 98
2 + 97
3 + 96
4 + 95
5 + 94
6 + 93
7 + 92
8 + 91
9 + 90
10 + 19
Keep going until we get to the point where the pairs of numbers start to reverse
48 + 51
49 + 50
51 + 48 ⇒ Here when the pairs start to reverse.
From 1 + 98 to 49 + 50 there are 49 pairs
Then from 51 + 48 to 98 +1 there are 48 pairs
Total pairs of whole numbers that add up to 99 is 49 + 48 = 97 pairs
