Multiple choice

The average (arithmetic mean) of a set of seven numbers is $8$. When an eighth number is added to the set, the average of the eight numbers is still $8$. What number was added to the set?

  1. $6$
  2. $7$
  3. $8$
  4. $9$
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C Correct answer
Explanation

Sum of 7 numbers = 7 * 8 = 56. Sum of 8 numbers = 8 * 8 = 64. The added number = 64 - 56 = 8.

AI explanation

The sum of the original seven numbers is 7 multiplied by 8 = 56. The sum of the new set of eight numbers is 8 multiplied by 8 = 64. The added number is the difference between these two sums, which is 64 - 56 = 8.

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