SOLUTION: There are 65 children in the sixth grade. There are 15 more boys than girls. How many girls are there in the class?

Suppose the teacher says to that class of 65:
 
"We have too many boys in this class.  We want our class to have exactly the
same number of girls as boys.  There are 15 more boys than girls.  Therefore to
make it even, 15 of you boys will have to leave and go to another class." 
 
Then 15 of the boys get up and leave the room.  Now the class has the same
number of girls as boys.
 
How many students are left in the room after the 15 boys leave?
 
65 - 15 = 50
 
So there are now only 50 students left in the room.  Half of those are girls
and half of them are boys.  Since one half of 50 is 25, there are 25 girls in
the class.

Edwin