Question

The sum of 1st 20 odd numbers is

Answer 1

Question

sum of first 20 odd numbers

Solution

1st 20 odd number

1,3,5,7,9.......39

Sn = n / 2 ( 2a + ( n - 1 ) d

first term = a = 1

common difference = d = 2

S 20 = 20 / 2 ( 2 (1) + ( 20 - 1 ) 2

=> 10 ( 2 + 38 )

=> 10 ( 40 )

=> 400

therefore, S20 = 400