Q5 of 84 Page 5

The sum of first 20 odd natural numbers is: (CBSE 2012)

Here A.P is 1,3, 5, ……


a= 1, d= 2 and n = 20


Sn = (2a + (n–1) d)


Sn = 20/2 (2 x 1 + (19) 2)


Sn = 10 (2 + 38)


Sn= 400

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