A) 80
B) 25
C) 20
D) 16
E) 4
Correct Answer: D
Solution :
\[\because \] Root mean square \[\ge \] Arithmetic mean \[\Rightarrow \] \[\sqrt{\frac{\sum\limits_{i=1}^{n}{x_{1}^{2}}}{n}}\ge 5\] \[\Rightarrow \] \[\sqrt{\frac{400}{n}}\ge 5\] \[\Rightarrow \] \[\frac{400}{n}\ge 25\] (squaring both sides) \[\Rightarrow \] \[n\le \frac{400}{25}=16\] \[\Rightarrow \] \[n=16\]
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