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    Question

    In a class, the ratio of number of boys to number of

    girls is 7:5. If 1 boy joined the class and 1 girl left the class, then the ratio becomes 5:3. Find the actual number of girls in the class.
    A 10 Correct Answer Incorrect Answer
    B 15 Correct Answer Incorrect Answer
    C 20 Correct Answer Incorrect Answer
    D 25 Correct Answer Incorrect Answer

    Solution

    Let initially the number of boys and girls be 7x and 5x, respectively.
    (7x + 1) : (5x − 1) = 5 : 3
    Or, 3(7x + 1) = 5(5x − 1)
    Or, 21x + 3 = 25x − 5
    Or, 4x = 8 ⇒ x = 2
    Therefore, number of girls = 5 × 2 = 10 

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