The sum of first 20 odd natural numbers is equal to :
Options:
A . 400
B . 210
C . 300
D . 420
Answer: Option A Answer: (a)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. $S_n =1/2n[2a + (n – 1)d]$Where a : First term; d : common difference$S_{20}= 1/2×20[(2×1) + (20 -1) × 2]$= 10 [2 + 38]=10 × 40 = 400Note :Sum of first n consecutive odd numbers = $n^2$
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