ABC26GN1535 · Average

Subject: General Aptitude · Chapter: Average · Exam: 2010 · Marks: · Difficulty:

The mean of the first ten even natural numbers is
(a)9
(b)10
(c)11
(d)12
Answer
Answer (as printed): C
Explanation
Required mean $=\left(\frac{2+4+6+\cdots+20}{10}\right)=\frac{2(1+2+\cdots+10)}{10}$ $$\begin{aligned} & =\left(\frac{1}{5} \times \frac{10 \times 11}{2}\right)=11 . \\ & \quad\left[\because 1+2+3+\cdots+n=\frac{n(n+1)}{2}\right] \end{aligned}$$

Explanation as extracted from the printed page; notation may be imperfect.

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