Multiple choice

In a set of three numbers, the average of the first two numbers is 4, the average of the last two numbers is 5, and the average of the first and the last numbers is 6. What is the average of three numbers?

  1. 30

  2. 5

  3. 15

  4. 3

  5. 2
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B Correct answer
Explanation

 Suppose the 3 numbers are A, B and C, so A + B = 2 x 4 = 8 ----------------- (1) B + C = 2 x 5 = 10 --------------- (2) A + C = 2 x 6 = 12 --------------- (3) On adding (1), (2) and (3), we get A + B + C = 15. Therefore, average = 15/3 = 5 

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