In a classroom of 33 students, the ratio of boys to girls is 3: 8. how many boys are in the class?
a: 12, since 38 of the students are boys
b: 11 , since 33 divided by 33 equals 11
c: 9 , since 3/11 of the students are boys
d: you cannot tell because you do not know the fraction of the total number of students that are boys.

X=number of boys
y=number of girls.

We can suggest the following system of equations:
x+y=33
x/y=3/8

We solve this system of equations by substitution method.
x/y=3/8       ⇒x=3y/8

(3y/8)+y=33
least common multiple=8
3y+8y=33*8
11y=33*8
y=(33*8)/11
y=3*8
y=24

x+y=33
x+24=33
x=33-24
x=9

number of boys /total number of students=9/33=3/11

There are 9 boys and 24 girls in the class. 

C: 9. since 3/11 of the students are boys.