The sum of first 20 odd natural numbers is equal to :

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The sum of first 20 odd natural numbers is equal to :

1. 210
2. 300
3. 400
4. 420

Correct Option: C

Series of first 20 odd natural numbers is an arithmetic progression with 1 as the first term and the common difference 2. Sum of n terms in arithmetic progression is given by.

S_n =	n	[2a + (n − 1)d]
	2

Where a = First term, d = common difference and n = Number of terms

∴ S₂₀ =	20	× [(2 × 1) + (20 − 1) × 2]
	2

∴ S₂₀ = 10 [ 2 + 38 ] = 10 × 40 = 400

Note : Sum of first n consecutive odd numbers = n²