Question

A student was asked to find the arithmetic mean of the numbers $3,11,7,9,15,13,8,19,17,21,14$ and x.He found the mean to be $12$ . what should be the number in place of x?

• A. $3$
• B. $7$
• C. $17$
• D. $31$

Answer 1

The correct option is B $7$

$Mean=\frac{\sum n}{n}$

Given, mean =12

$\therefore 12=\frac{3+11+7+9+15+13+8+19+17+21+14+x}{12}$

$12=\frac{137+x}{12}$

$144=137+x$

$\therefore x=144-137=7$