algebra

Classes A and B have 35 students each. If seven girls shift from class A to class B, then the number of girls in the classes would interchange. If four girls shift from class B to class A, then the number of girls in class A would be twice the original number of girls in class B. What is the number of boys in class A and class B?

Please help. I'm not able to form a correct equation to solve.

asked by nimal
  1. I am assuming that the 2nd shift follows the first shift

    now:
    let the number of girls in A be x
    let the number of girls in B be y

    after 1st shift:
    A has x-7
    B has y+7
    "the number of girls in the classes would interchange"
    ---> y+7 = x

    2nd shift
    A has x-7 + 4 = x-3
    B has y+7 - 4 = y-3
    " the number of girls in class A would be twice the original number of girls in class B"
    --> x-3 = 2y or x = 2y+3

    so 2y+3 = y+7
    y = 4
    x = 11

    so originally, there were 24 boys in A and 31 in B

    posted by Reiny

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