Help Please :) Fractions

[sburdic]

Two thirds of Mrs. Scott's class were boys. One day twin girls joined the class. Now three fifths of the class is boys. How many children are in Mrs. Scott's class now?
I have tried making equations, but I don't think it is write. I had the equation
(2/3)-x=(3/5)
Thanks so much!!

 

[Loren]

Certainly there are more than one way to solve this.
First, you have to learn to name things. Write down what x stands for. Is it "x = the number in the class before the twins joined" or "x= number in the class after twins joined"? It can be either. You might consider choosing the one that leads to the question asked. Once you have that decided you are ready to build your phrases that will lead to an equation.
I'll try to get you started.
If you say ...
Let x represent the number of students in the class after the twins joined.
Then x-2 represents the number before the twins joined.
You know that 2/3 of the class before the twins joined were boys. Write an expression that says that.
You know that 3/5 of the class after the twins joined were boys. Write another expression that says this.
Now you should have two expressions about the number of boys in the class.
You know that the number of boys has not changed. That should be the basis of your equation.
Good luck.

 

[artluvr77]

i think its 2/3+x=3/5
because when the 2 girls were added it became 3/5 not when they were subtracted.
good luck

 

[Denis]

As is: b / (b+g) = 2/3 ; simplify: b = 2g [1]
Add 2 g: b / (b+g+2) = 3/5 ; simplify: 2b = 3g + 6 [2]

Substitute [1] in [2] : solve to get g=6, b=12