To Find: The sum of all odd integers from 1 to 201.

The odd integers form the following AP series:

1,3,5….201

First term = a = 1

Common difference = d = 2

Last term = 201

Let the number of terms be n

⇒1 + 2(n - 1) = 201

⇒n - 1 = 100

⇒n = 101

= 101 × 101 = 10201

The sum of all odd integers from 1 to 201 is 10201.