Question 42

waecmaths question: 

Calculate the variance of 2, 4, 7, 8 and 9

Option A: 

7.2

Option B: 

7.8

Option C: 

3.5

Option D: 

2.6

waecmaths solution: 

$\begin{align}  & mean=\bar{x}=\frac{2+4+7+8+9}{5} \\ & \bar{x}=\frac{30}{5}=6 \\ & variance={{\sigma }^{2}} \\ & {{\sigma }^{2}}=\frac{{{\left| 2-6 \right|}^{2}}+{{\left| 4-6 \right|}^{2}}+{{\left| 7-6 \right|}^{2}}+{{\left| 8-6 \right|}^{2}}+{{\left| 9-6 \right|}^{2}}}{5} \\ & {{\sigma }^{2}}=\frac{16+4+1+4+9}{5}=\frac{34}{5}=6.8 \\\end{align}$

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