A) \[6.5\]
B) 7
C) 7.5
D) 8
Correct Answer: A
Solution :
(a): A.M \[=\frac{\sum{xi}}{n}=\frac{2+........11}{10}=\frac{\left\{ \left( 1+...........11 \right)-1 \right\}}{10}\] \[{}^{=\left\{ \left( \frac{11\times 12}{2} \right)-1 \right\}}/{}_{10=\frac{65}{10}=6.5}\] We have purposely written it like this so that we get Gaussian identity. Which is sum of first 'n' natural numbers \[=\frac{n\left( n+1 \right)}{2}\]
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