Multiple choice

A student was asked to find the average of the following $12 $ numbers :$ 3, 11, 7, 9 , 15, 13, 8, 19, 17, 21, 14\ and \ x.$ He found the average to be $12$. What should come in place of x?

  1. $3$
  2. $7$
  3. $17$
  4. $31$
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B Correct answer
Explanation

Sum of 11 numbers (3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14) is 137. Total sum for 12 numbers with average 12 is 144. Thus, x = 144 - 137 = 7.

AI explanation

The formula for average states that the sum of the numbers equals the average multiplied by the count. The total sum of the 12 numbers is 12 times 12 = 144. The sum of the 11 given numbers is 3 + 11 + 7 + 9 + 15 + 13 + 8 + 19 + 17 + 21 + 14 = 137. Subtracting this sum from the total gives x, so x = 144 minus 137, which equals 7. The value of x is 7.

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