Question

How many pairs of whole numbers have a sum of 99

Answer 1

50

0+99
1+98
....
....
49+50

Then stop
because 49+50 is the same pair as 50+49 and 51+48 is the same as 48+51 (already counted)

Answer 2

Answer : 50

Question says whole number , so we start with 0

0 + 99 = 99  (0,99)

1 + 98 = 99    (1,98)

2 + 97 = 99  (2,97)

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-

49 + 50 = 99  (40,50)

We will get the same sum , if we put the numbers in reverse

50 + 49 = 99

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99 + 0 = 99

So there are 50 pairs of whole numbers have a sum of 99