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    Question

    In a school, the average number of books that some numbers of boys have is 100 and average number of books that some numbers of girls have is 70. If each boy have 5 books then the average numbers of books with all the students become 80. The total number of boys is what percentage of the total number of students in that school?

    A 30% Correct Answer Incorrect Answer
    B 40% Correct Answer Incorrect Answer
    C 50% Correct Answer Incorrect Answer
    D 60% Correct Answer Incorrect Answer
    E 70% 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 = 100x The total number of books the girls have = 70y If each of the boy have 5 books, then the remaining number of books = 100x – 5x = 95x The sum of the all the books = 80(x + y) = 95x + 70y 10y = 15x x : y = 2 : 3 Required % = (2/5) × 100 = 40%

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