There are infinitely many sets:
For example,
-99, -98, -97, ... -2, -1, 0, 1, 2, ... 97, 98, 99, 100
or
1, 1, 1, 1 ... [100 times]
or 0.0001, 0.0001, 0.0001, ... [ a million times].
100
5050
102*25=2550
62.5 and 37.5
if you add all the numbers up and dived them by the numbers of numbers
100
5050
-99
102*25=2550
5050, ie (1 + 100) x (100/2)
You can either just add them up or use quick logic to add them in pairs: All the numbers from 1 to 49 match up with 51 through 99 to = 49 pairs of 100 = 4900, than add the two you skipped 4900 + 50 + 100 = 5050 total
36 and 64
103
The even numbers up to 100 are: 2 468101214161820222426283032343638404244464850525456586062646668707274767880828486889092949698100.
30
53+47
62.5 and 37.5