There were 25 students in an algebra class. if the number of girls is 10 more than half the number of boys, how many boys were in the class?

There are 25 students. 

Let g = girls, and b = boys

g = 1/2b + 10

g + b = 25

Plug in 1/2b + 10 for g

(1/2b + 10) + b = 25

3/2b + 10 = 25

isolate the b, subtract 10 from both sides, and then multiply by 2/3

3/2b + 10 (-10) = 25 (-10) 

3/2b = 15

(3/2b)/(2/3) = 15(2/3)
b = 30/3
b = 10

Subtract 10 from 25 to get the number of girls

25 - 10 = 15

g = 15

There are 10 boys in the class.

hope this helps