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    Question

    In a school, the average number of books that some

    numbers of boys have is 120 and average number of books that some numbers of girls have is 90. If each boy has read 5 books, then the average numbers of unread books with all the students become 100. The total number of boys is what percentage of the total number of students in that school?
    A 40% Correct Answer Incorrect Answer
    B 20% Correct Answer Incorrect Answer
    C 25% Correct Answer Incorrect Answer
    D 36% Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the total number of boys be x. and the total number of girls be y. The total number of books boys have = 120x The total number of books the girls have = 90y If each of the boy have read 5 books, then the remaining number of unread books = 120x – 5x = 115x The sum of the all the books = 100(x + y) = 115x + 90y 2y = 3x x : y = 2 : 3 Required % = (2/5) × 100 = 40%

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