ABC26GN1536 · Average

Subject: General Aptitude · Chapter: Average · Exam: 2009 · Marks: · Difficulty:

The arithmetic mean of first 11 natural numbers is
(a)5
(b)5.5
(c)6.0
(d)6.5
Answer
Answer (as printed): C
Explanation
Required mean $=\left(\frac{1+2+\cdots+11}{11}\right)=\left(\frac{1}{11} \times \frac{11 \times 12}{2}\right)=6$. $$\left[\because 1+2+\cdots+n=\frac{n(n+1)}{2}\right]$$

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

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