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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 85. If each boy has 5 books then the average numbers of 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 20 Correct Answer Incorrect Answer
    B 30 Correct Answer Incorrect Answer
    C 40 Correct Answer Incorrect Answer
    D 50 Correct Answer Incorrect Answer
    E 60 Correct Answer Incorrect Answer

    Solution

    Let the total number of boys be x.  The total number of girls be y. The total number of books boys have = 120x The total number of books the girls have = 85y If each of the boy have 5 books, then the remaining number of books = 120x – 5x = 115x The sum of the all the books = 100(x + y) = 115x + 85y y = x x : y = 1 : 1 Required % = (1/2) × 100 = 50%

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