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    Question

    Out of four numbers the average of the first three is 16

    and that of the last three is 15. If the last number is 20 then the first number is
    A 25 Correct Answer Incorrect Answer
    B 28 Correct Answer Incorrect Answer
    C 23 Correct Answer Incorrect Answer
    D 21 Correct Answer Incorrect Answer

    Solution

    Let three numbers be a, b and c respectively ∴  a + b + c = 16 × 3 = 48 ….(i) b + c + 20 = 15 × 3 = 45  b + c = 45 – 20 = 25 …..(ii) By equation (i) – (ii) a = 48 – 25 = 23

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