Question

If the mean of 5, 7, x, 10, 5 and 7 is 7, then x =

(a) 6 (b) 7 (c) 8 (d) 9

Answer 1

Here, the observations are 5, 7, x, 10, 5 and 7.
$$\begin{gathered} \mathrm{Mean}=\frac{\mathrm{Sum}\mathrm{of}\mathrm{observations}}{\mathrm{Number}\mathrm{of}\mathrm{observations}} \\ \Rightarrow 7=\frac{5+7+x+10+5+7}{6} \\ \Rightarrow x+34=42 \\ \Rightarrow x=42-34=8 \end{gathered}$$
Hence, the correct option is (c).