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.
`s_n` = `n/2`[ 2a + (n - 1)d] = `45/2` x [2 x 1 + (45- 1) x 1] = ( `(45)/(2)` x 46 ) = ( 45 x 23)
= 45 x (20 + 3 ) = (45 x 20 + 45 x 3) = (900 + 135) = 1035
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