Question 1201509
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There were twice as many boys as girls in a Swimming Club. 
After 40 boys and 15 girls left the club, the number of girls who remained 
was 3/5 of the number of boys who remained in the club. 
How many children were there in the club at first?
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Originally  x girls ans 2x boys.
The number x is unknown, and our goal is to find x.


Agter After 40 boys and 15 girls left the club,
(x-15) girls and (2x-40) boys remained.


The problem dictates us this proportion

    {{{(x-15)/(2x-40)}}} = 3/5.


To solve it, first cross multiply

    5(x-15) = 3*(2x-40).


Next simplify and find x

    5x - 75 = 6x - 120

    120 - 75 = 6x - x

       45    =    x.


<U>ANSWER</U>.  Originally, there were 45 girls and 2*45 = 90 boys.

         The total was 45 + 90 = 135 children.
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Solved.