Class 4Y and Class 4Z have a total of 36 students. ¹₅ of the students in Class 4Y and ³₇ of the students in Class 4Z are boys. The number of girls in Class 4Y is equal to the number of girls in Class 4Z. Find the total number of girls in the 2 classes.
Fraction of Class 4Y that are girls
= 1 - ¹₅ 
= ⁴₅

Fraction of Class 4Z that are girls
= 1 - ³₇ 
= ⁴₇ 
 
The number of girls in Class 4Y is equal to the number of girls in Class 4Z.

The numerators are the same.  

⁴₅ Class 4Y = ⁴₇ Class 4Z 

Number of students in Class 4Y = 5 u
Number of students in Class 4Z = 7 u

Total number of students 
= 5 u + 7 u
= 12 u

12 u = 36

1 u = 36 ÷ 12 = 3

Number of girls in Class 4Y =4 u
Number of girls in Class 4Z =4 u

Total number of girls
= 4 u + 4 u
= 8 u
= 8 x 3
= 24

Answer(s): 24