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    Question

    Average of first 3 numbers is half the average of next 6

    numbers. If the average of all 9 numbers is 15, find the sum of the last 6 numbers.
    A 108 Correct Answer Incorrect Answer
    B 72 Correct Answer Incorrect Answer
    C 81 Correct Answer Incorrect Answer
    D 90 Correct Answer Incorrect Answer
    E 96 Correct Answer Incorrect Answer

    Solution

    Let the sum of the last 6 numbers be 'n'.
    (sum of first 3 numbers) ÷ 3 = 0.5 × (n/6)
    ⇒ Sum of first 3 numbers = 0.25n
    Total sum = n + 0.25n = 1.25n
    Average of 9 numbers = 1.25n ÷ 9 = 15
    ⇒ 1.25n = 135
    ⇒ n = 108

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