Question

If the mean of observations 7, 8, 9, 11 and x is 10, then x =

(a) 10 (b) 15 (c) 12 (d) 13

Answer 1

Given : the mean of the observations 7, 8, 9, 11 and x is 10.
$$\begin{gathered} \mathrm{Mean}\mathrm{of}\mathrm{observations}=\frac{\mathrm{Sum}\mathrm{of}\mathrm{observations}}{\mathrm{Number}\mathrm{of}\mathrm{observations}} \\ \Rightarrow 10=\frac{7+8+9+11+x}{5} \\ \Rightarrow 35+x=50 \\ \Rightarrow x=50-35=15 \end{gathered}$$
Thus, the value of x is 15.
Hence, the correct option is (b).