question_answer

A student was asked to find the arithmetic mean of the following 12 numbers 3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14, and x. He found the mean to be 12. The value of x will be

A) 3                                 

B) 7

C) 17                                

D) 31

Correct Answer: B

Solution :

Arithmetic mean \[=\frac{\text{Sum}\,\text{of}\,\text{total}\,\text{numbers}}{\text{Total}\,\text{number}\,\text{of}\,\text{terms}}\]

\[12=\frac{3+11+7+9+15+13+8+19+17+21+14+x}{12}\]      \[144=137+x\]

\[x=144-137\]

\[\therefore \]      \[x=7\]