ABC26GN1553 · Average

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

The mean of $1^{2}, 2^{2}, 3^{2}, 4^{2}, 5^{2}, 6^{2}, 7^{2}$ is
(a)10
(b)20
(c)30
(d)40
Answer
Answer (as printed): B
Explanation
$1^{2}+2^{2}+3^{2}+\ldots+n^{2}=\frac{n(n+1)(2 n+1)}{6}$. $$\therefore 1^{2}+2^{2}+3^{2}+\ldots+7^{2}=\left(\frac{7 \times 8 \times 15}{6}\right)=140 .$$ So, required average $=\left(\frac{140}{7}\right)=20$.

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

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