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    Question

    The average of 12 numbers is 48. The average of the

    first 5 numbers is 45 and the average of next 4 numbers is 52. If the 10th number is 10 less than the 11 th number and is 5 more than the 12th number, then the average of the 11 th and 12th numbers is: 
    A 50.5 Correct Answer Incorrect Answer
    B 46.5 Correct Answer Incorrect Answer
    C 47.5 Correct Answer Incorrect Answer
    D 48.5 Correct Answer Incorrect Answer

    Solution

    Average of 12 numbers = 48 → Sum = 576 Average of first 5 numbers = 45 → Sum = 225 Average of next 4 numbers = 52 → Sum = 208 Let 10th number = x, 11th number = x + 10, 12th number = x − 5 225 + 208 + 3x + 5 = 576 3x + 438 = 576   ⟹   x = 46 11th number = 56, 12th number = 41 Average = (56 + 41)/2 = 48.5  

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