Find the sum 1 + 2 + 3 + 4 + 5 + ...................... + 100

We have to find the sum of 1+2+3+4….upto…100.

We see these numbers are in AP having common difference of 1.

So we apply here the formula :- Sⁿ = n/2 (a + l)

Here a = 1. l = 100 n = 100

Sⁿ = 100/2 (1 + 100)

= 100/2 (101)

= 50 × 101

= 5050.

Sum of 1+2+3+4……100 is 5050.