Sum of first hundred natural numbers?

The sum of the first n natural numbers is given by Gauss' formula:

n(n + 1)/2.

Here, n = 100, so the sum is

100*101/2 = 5050.

you can do the following:
0+100=100
1+99=100
2+98=100
3+97=100
.
.
.
.
49+51=100

so, the sum is 50*100+50=5050

We have a formula to count first n natural numbers as
n(n-1)/2
Here n=100
so
sum is
100(100-1)/2=100(99)/2
=9900/2=4950

Gauss did it when he was 6 years old.
Sum=n/2(1st + last)=50(101)=5050

(total terms)(first term + last term)/2

1 + 2 + 3 + 4 + 5 + ...... + 100
= 100(1 + 100)/2
= 100(101)/2
= 10100/2
= 5050