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    Question

    Average of first 3 numbers is three times the average of

    next 6 numbers. If the average of all nine numbers is 15, find the sum of the last 6 numbers.
    A 48 Correct Answer Incorrect Answer
    B 54 Correct Answer Incorrect Answer
    C 60 Correct Answer Incorrect Answer
    D 66 Correct Answer Incorrect Answer
    E 72 Correct Answer Incorrect Answer

    Solution

    Let the sum of the last 6 numbers be 'n'.
    (sum of first 3 numbers) ÷ 3 = 3 × (n/6)
    ⇒ Sum of first 3 numbers = 1.5n
    Total sum = n + 1.5n = 2.5n
    Average of 9 numbers = 2.5n ÷ 9 = 15
    ⇒ 2.5n = 135
    ⇒ n = 54

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