Question

Mean of $5$ observation is $7$. If four of these observation are $6,7,8,10$ and one is missing then the variance of of all the five observations is :

• A. $4$
• B. $6$
• C. $8$
• D. $2$

Answer 1

The correct option is A $4$

Let missing number be $x$

$Mean=\frac{sumofobservation}{numberofobservation}$

$\Rightarrow 7=\frac{6+7+8+10+x}{5}$

$\Rightarrow 7\times 5=31+x$

$\Rightarrow x=35-31$

$\therefore x=4$

So, the missing number is $4$

Hence $A$ is the correct answer.