Question
The sum of all even natural numbers between 1 and 31 is
Answer: Option C
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Required sum = ( 2 + 4 + 6 + ..............+ 30)
This is an A.P. in which a = 2, d = (4 - 2) = 2 and `l` = 30.
Let the number of terms be n. Then
`t_n` = 30 `rArr` a + (n - 1) d = 30
`rArr` 2 + (n - 1) x 2 = 30 `rArr` n - 1 = 14 `rArr` n = 15
`:.` `S_n` = `n/2` ( a + `l`) = `15/2` ( 2 + 30) = 240
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The sum of first 45 natural numbers is :
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