The mean of first n natural numbers is equal to \frac{n+7}{3}, then 'n' is equal to

NIMCET 2011 Question Paper with solutions

Question : 35 of 120

Marks: +1, -0

The mean of first

n

natural numbers is equal to

\;{n+7}/{3}

, then 'n' is equal to

Solution:

Since, mean

= {n+7}/{3}

∴ {1+2+. . .+n}/{n}= {n+7}/{3}

⇒ {n(n+1)}/{2 n}=\;{n+7}/{3}

⇒ 3 n+3=2 n+14

⇒ \ n=11

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