Question

The mean of seven numbers is 63. If the six numbers are 65, 70, 68, 59, 73, 55. Find the seventh number.

Answer 1

Let the seventh number be x.
Now,

$$\begin{gathered} \mathrm{Mean}=\frac{\mathrm{Sum}\mathrm{of}\mathrm{observations}}{\mathrm{Number}\mathrm{of}\mathrm{observations}} \\ \Rightarrow 63=\frac{65+70+68+59+73+55+x}{7} \\ \Rightarrow 63=\frac{390+x}{7} \\ \Rightarrow 390+x=441 \\ \Rightarrow x=441-390=51 \end{gathered}$$