Let x represent the number of boys.
Then 1/2x + 10 represents the number of girls. (there are 10 more than half the number of boys)
We can set up a simple equation for this situation:
# of boys + # of girls = 25 students
so
x + (1/2x + 10) = 25
x + 1/2x + 10 = 25
1/2 = 0.5
x + 0.5x + 10 = 25
1.5x + 10 = 25
1.5x = 25 - 10
1.5x = 15
x = 15/1.5
x = 10
x = # of boys, so there are 10 boys in the class.
Good luck on your math!
-Jabba