SOLUTION: The ratio of the number of boys to the number of girls in a class of 42 pupils was 4:3 when some boys left the class the number of girls was the same as the number of boys. how man

Question 1090635: The ratio of the number of boys to the number of girls in a class of 42 pupils was 4:3 when some boys left the class the number of girls was the same as the number of boys. how many boys left the class
Answer by ikleyn(52781) (Show Source): You can put this solution on YOUR website!
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Let x = be the number of boys in the class, and y be the number of girls.

Then you have two equations:

 = ,

x + y = 42.

Express x via y from the first equation: x = , and substitute it into the second equation. 
You will get a single equation for the unknown y:

 + y = 42.

Multiply both sides by 4 and simplify.

4y + 3y = 42*3 = 126,

7y = 126, 

y =  = 18.

Now x =  =  = 24.

Answer. There are 24 boys and 18 girls in the class.

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