Question 27

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waecmaths question: 

Given that the mean of the scores 15, 21, 17, 26, 18 and 29 is 21. Calculate the standard deviation of the scores.

Option A: 

$\sqrt{10}$

Option B: 

4

Option C: 

5

Option D: 

$\sqrt{30}$

waecmaths solution: 

\[\begin{align}  & \bar{x}=\frac{15+21+17+18+26+29}{5}=21 \\ & variance=\frac{\left( {{(15-21)}^{2}}+{{(21-21)}^{2}}++{{(18-21)}^{2}}{{(17-21)}^{2}}+{{(26-21)}^{2}}+{{(29-21)}^{2}} \right)}{5} \\ & variance=\frac{36+0+9+16+25+64}{5}=\frac{150}{5} \\ & variance=30 \\ & s.d=\sqrt{30} \\\end{align}\]

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