If the sum of the first 2 n terms of 2 , 5 , 8 , …… is equal to the sum of the first n terms of 57,59 , 61 …… . , then n is equal to

Given, 2 2 n { 2.2 + ( 2 n − 1 ) 3 } = 2 n { 2.57 + ( n − 1 ) 2 } or 2 ( 6 n + 1 ) = 112 + 2 n or 10 n = 110 , ∴ n = 11

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MathematicsSequence & SeriesA.P.Medium2 minPYQ_2011

MathematicsMediumsingle choice

If the sum of the first $2 n$ terms of $2, 5, 8, \dots\dots$ is equal to the sum of the first $n$ terms of 57,59 , $61 \dots\dots$ . , then $n$ is equal to

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Solution:

Given, $\frac{2 n}{2} {2.2 + (2 n - 1) 3} = \frac{n}{2} {2.57 + (n - 1) 2}$ or $2 (6 n + 1) = 112 + 2 n$ or $10 n = 110, ∴ n = 11$

Stream:BITSATSubject:MathematicsTopic:Sequence & SeriesSubtopic:A.P.

⏱ 2mℹ️ Source: PYQ_2011

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