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    Question

     The average of 21 numbers is 77. The average of the

    first 11 numbers is 74, and the 0 average of the last 11 numbers is 84. If the 11th number is excluded, then the average of the remaining numbers is:
    A 74.8 Correct Answer Incorrect Answer
    B 78.5 Correct Answer Incorrect Answer
    C 76.3 Correct Answer Incorrect Answer
    D 72.4 Correct Answer Incorrect Answer

    Solution

    Total sum of 21 numbers = 21 × 77 = 1617

    Sum of first 11 numbers = 11 × 74 = 814

    Sum of last 11 numbers = 11 × 84 = 924

    Now, the 11th number is common in both groups, so

    11th number = 814 + 924 − 1617 = 121

    If the 11th number is excluded, sum of remaining 20 numbers = 1617 − 121 = 1496

    Required average = 1496/20 = 74.8

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