Multiple choice

In seven given numbers, the average of the first four numbers is 4 and that of the last four numbers is also 4. If the average of these seven numbers is 3, the fourth number is

  1. 3

  2. 4

  3. 7

  4. 11
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D Correct answer
Explanation

Sum of 7 numbers = 7 * 3 = 21. Sum of first 4 = 4 * 4 = 16. Sum of last 4 = 4 * 4 = 16. Sum of all 7 = (Sum of first 4) + (Sum of last 4) - (4th number) = 16 + 16 - x = 21. 32 - x = 21, so x = 11.

AI explanation

The sum of the first four numbers is 4 times 4, which equals 16. The sum of the last four numbers is also 16. The total sum of all seven numbers is 7 times 3, which equals 21. Because the fourth number is counted in both the first four and the last four sums, it is equal to the combined sum of both groups minus the total sum of all seven numbers, calculated as (16 + 16) - 21, resulting in 11.

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