A) 124
B) 127.5
C) 130
D) 133.5
Correct Answer: C
Solution :
[c] \[\because \] Average of the square of the first 19 natural number \[=\frac{n\,\,(n+1)\,\,(2n+1)}{6n}\] \[\Rightarrow \frac{19\,\,(19+1)\,\,(19\times 2+1)}{6\times 19}\] \[\frac{19\times 20\times 39}{\begin{align} & 6\times 19 \\ & \Rightarrow \,\,130 \\ \end{align}}\]
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