An infinite number.
There are infinitely many pairs. For example 23.5 and 75.5 or -3 and 102.
If you include negative numbers, the list is infinite.
The sum of whole numbers 1 through 30 is 465.
The sum of the first five whole numbers is 10.
100
20 of them
An infinite number.
3 pairs of whole numbers add up to 7: 1 +6, 2+5, 3+4 (0+7 also equals 7, but zero is not a whole number)
6
49 of them.
There 4 pairs of primes that can give a sum 40 in addition. They are (3,37), (11,29), (17,23),(19,21).
100
Only one pair.
Just 3 + 3
number of pairs of odd numbers whose sum is 32: 8pairs of odd numbers whose sum is 32:1, 313, 295, 277, 259, 2311, 2113, 1915, 17
There are two pairs of prime numbers that express 18 as the sum of two prime numbers: 7 + 11 = 18 and 5 + 13 = 18.