Multiple choice

The average of 8 numbers is 20. The average of first two numbers is $15\frac{1}{2}$ and that of the next three is $21\frac{1}{3}$. If the sixth number be less than the seventh and height numbers by 4 and 7 respectively, then the eight number is:

  1. 18

  2. 22

  3. 25

  4. 27
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A Correct answer
AI explanation

The sum of all 8 numbers is 8 multiplied by 20, equaling 160. The sum of the first two is 2 multiplied by 15.5, which is 31, and the sum of the next three is 3 multiplied by 21.33, which is 64. The sum of the remaining three numbers is 160 minus 31 plus 64, giving 65. Let the sixth number be x, making the seventh x plus 4 and the eighth x plus 7. The equation x plus x plus 4 plus x plus 7 equals 65 results in 3x equaling 54, so x is 18; therefore, the eighth number is 25.

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