First 100 postive numbers are:
1, 2, 3,4,5, ……………………. 100.
These number are in AP.
Sum of AP is given by,
{n * (a + l) /2} [Where a = first term, n = number of terms, l = last term.]
= 100 * (1 +100)/2 = 50 * 101.
Required Average = (50 *101)/100 = 50.5.