Question
The sum of first 45 natural numbers is :
Answer: Option A
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Let `S_n` = (1 + 2 + 3 +..............+ 45)
This is an A.P. in which a = 1, d= 1, n = 45 and ` l` = 45
`:.` `S_n` = `n/2` ( a + `l`) = `45/2` x (1 + 45) = ( 45 x 23) = 45 x (20 + 3)
= ( 45 x 20) + (45 x 3) = 900 + 135 = 1035
Required sum = 1035.
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