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28 September, 04:20

Some girls and some boys are raising money for a trip to China. there was 40% girls. after two girls left and two boys came, there was 30% girls. what was the original amount of girls?

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Answers (2)
  1. 28 September, 04:27
    0
    The original amount is 20% of girls
  2. 28 September, 04:38
    0
    For an instance, g represents the original amount of girls and b represents the original amount of boys.

    Write an equation based on the problem

    There was 40% girls, the equation will be

    g = 40% (b + g)

    first equation

    If two girls left and two boys came, there was 30% girls, the equation will be

    g - 2 = 30% (b + 2 + g - 2)

    second equation

    Work on the first equation

    To make it easier in calculation, change percent into decimals

    g = 40% (b + g)

    g = 0.4 (b + g)

    g = 0.4b + 0.4g

    Work on the second equation

    Change percent into decimals and simplify the equation

    g - 2 = 30% (b + 2 + g - 2)

    g - 2 = 0.3 (b + g)

    g = 0.3b + 0.3g + 2

    Solve the equation system by substitution method

    g = g

    0.4b + 0.4g = 0.3b + 0.3g + 2

    0.1b + 0.1g = 2

    0.1 (b + g) = 2

    b + g = 20

    The original amount of boys and girls is 20

    Find the original amount of girls

    Original amount of girls is equal to 40% of the original amount of boys plus girls.

    g = 0.4 (b + g)

    g = 0.4 (20)

    g = 8

    The original amount of girls is 8
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