a= 1
d = 3-1 = 2
n = 20
Sn = n/2 [ 2a (n - 1 ) d ]
S20 = 20/2 [2(1) (20-1)(2)]
= 10[2 (19*2)]
= 10(2 38)
= 10(40)
= 400
Written on April 6, 2019, 9:41 a.m.
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Answer of this question
The sum of first 20 odd numbers is ?
Ap: 1,3,5,7,...........,37,39
a= 1
d = 3-1 = 2
n = 20
Sn = n/2 [ 2a (n - 1 ) d ]
S20 = 20/2 [2(1) (20-1)(2)]
= 10[2 (19*2)]
= 10(2 38)
= 10(40)
= 400
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