Question

The mean of 10 numbers is 55. If one number is excluded, their mean becomes 50, find the excluded number.

Answer 1

Let the sum of $10$ numbers be x

So $\frac{x}{10}=55$

$\Rightarrow x=550$

Let the excluded no. be y

So $\frac{x-y}{9}=50$

$\Rightarrow x-y=450$

$\Rightarrow y=550-450$

$\Rightarrow y=100$.