Correct Answer - Option 2 : 7
Given
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.
Concept used
Average
Calculation
Mean means average
Mean = 12 (Given)
⇒ \(\frac{{3 + 11 + 7 + 9 + 15 + 13 + 8 + 19 + 17 + 21 + 14 + x}}{{12}} = 12\)
⇒ 137 + x = 144
⇒ x = 7