SOLUTION: The ratio of boys to girls in a class is 3:4.I f there are 42 pupils in class, how many are girls?

Question 1006067: The ratio of boys to girls in a class is 3:4.I f there are 42 pupils in class, how many are girls?
Answer by ikleyn(52787) (Show Source): You can put this solution on YOUR website!
.

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.

3y + 4y = 42*4 = 168,

7y = 168, 

y =  = 24.

Now x =  =  = 18.

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

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