What is sum of the first 100 whole numbers?

Answer 1

It is instructive to note that you can rewrite 1+2+3+4....+99+100 as 1+100+2+99+3+98....+50+51

Then you can group each pair of numbers as (1+100)+(2+99)+(3+98)+...+(50+51)

All of these couplets add up to 101, and there are 50 of them. Thus the sum of the first 100 whole numbers is 50x101. This can be calculated at 5,050.