Question

fifty percent of the students in a class are boys there are 15 boys in the class how many total students are in the class

Answer 1

50%=1/2
2 is commonly used to convey half
15*2=30
There are 30 total student in the class

Answer 2

50% is half, so if 50% of the students or male, half are male. 
15 males are half the class, then the other half must be 15 females. Add them together and you have 30!
answer : 30