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Question 600119: there are 25 children in the class: 3/5 of the children are boys. how many girls are in the class?
Answer by godsgirls(5)   (Show Source):
You can put this solution on YOUR website! This is actually pretty simple if you know how to create proportions and use cross-multiplication. I'll show you.
There are 25 children in the class. 3/5 are boys. How many are girls?
Well, right away, we can see that if 3/5 are boys, then obviously, the other 2/5 are girls. So we write a proportion.
There are 25 children in all. Therefore, 25 goes on the bottom. We know that 3/5 of those 25 are boys, but we only want to find the girls, so we'll use the 2/5 fraction here. 
now, we want to find x, because x tells us how many girls there are. We know that the fraction x/25 is equal to 2/5. But they need a common denominator. Therefore, by multiplying 2/5 by 5, we get 10/25 
Here we've just proven that 2/5 equals 10/25. Therefore, there are 10 girls in the class of 25 students (and that means there are, by subtraction, 15 boys.)
I hope this helps you!
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