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    Question

    The ratio of the number of girls to the number of

    boys in a school of 720 students is 3 : 5. If 18 boys left the school, find how many new girls may be admitted so that the ratio of number of girls to the number of boys may change to 2 : 3.
    A 18 Correct Answer Incorrect Answer
    B 20 Correct Answer Incorrect Answer
    C 19 Correct Answer Incorrect Answer
    D 28 Correct Answer Incorrect Answer

    Solution

    Ratio of number of girls to the number of boys= 3:5 Sum of the terms of the ratio = 3 + 5= 8 `:.` The number of girls in the school =`(3)/(8)` x 720 = 270 and the number of boys in the school = `(5)/(8)` x 720 = 450 Let the number of new girls admitted be x, then the number of girls become (270 + x) After 18 boys leave the school, the number of boys become (450 -18) i.e. 432 According to given, `(270 + x)/(432)= (2)/(3)` `rArr` 270 + x = 2`xx` 144 `rArr` 270 + x = 288 `rArr` x = 18

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