Question 708806
Let x=number of children in the class
If the ratio is 2:3 this means that out of every 2+3=5 children
2/5 are boys and 3/5 are girls, so 
(2/5)x=10  multiply each side by (5/2)
x=25----number of children
25-10=15----number of girls
CK
2:3=10:15-----OK

Hope this helps---ptaylor