well we can set up this proportion.
2 boys
---------
3 girls
Now lets add this together to equal a smaller proportion class.
2 boys + 3 girls = 5 students.
We need for their to be 30 students.
So what number can we multiply them by to get 30 students in all when added.
Well we can divide 30 ÷ 5 = 6
so multiply each number.
2 boys x 6 = 12
3 girls x 6 = 18
these two numbers add up to 30 and when this fraction is simplified it is 2/3
So your finally answer is....
12 boys and 18 girls.
Good Luck! :)