Question
( 6 + 15 + 24 + 37 + ........................+ 105 ) = ?
Answer: Option C
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Given series in an A.P. in which a = 6, d = (15 - 6) = 9 and `l` = 105.
Let the number of terms in it be n . Then ,
`a + (n - 1)d = 105`
`rArr` 6 + (n - 1) x 9 = 105
`rArr` (n - 1) x 9 = 99
`rArr` (n - 1) = 11
`rArr` n = 12
Required sum = `n/2 (a + l) = 12/2 ( 6 + 105)` = (6 x 111) = 666.
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