Multiple choice general knowledge math & puzzles

The mean of the numbers a, b, 8, 5, 10 is 6 and the variance is 6.80. Then which one of the following gives possible values of a and b?

  1. a = 0, b = 7

  2. a = 5, b = 2

  3. a = 3, b = 4

  4. a = 2, b = 4
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C Correct answer
Explanation

Mean: (a+b+8+5+10)/5 = 6 => a+b=7. Variance: [a^2+b^2+8^2+5^2+10^2]/5 - 6^2 = 6.8 => a^2+b^2+189 = 5(42.8) = 214 => a^2+b^2=25. If a+b=7 and a^2+b^2=25, the values are 3 and 4.

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