Class 2X and Class 2Y have a total of 72 students. ¹₅ of the students in Class 2X and ³₇ of the students in Class 2Y are boys. The number of girls in Class 2X is equal to the number of girls in Class 2Y. Find the total number of girls in the 2 classes.
Fraction of Class 2X that are girls
= 1 - ¹₅ 
= ⁴₅

Fraction of Class 2Y that are girls
= 1 - ³₇ 
= ⁴₇ 
 
The number of girls in Class 2X is equal to the number of girls in Class 2Y.

The numerators are the same.  

⁴₅ Class 2X = ⁴₇ Class 2Y 

Number of students in Class 2X = 5 u
Number of students in Class 2Y = 7 u

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

12 u = 72

1 u = 72 ÷ 12 = 6

Number of girls in Class 2X =4 u
Number of girls in Class 2Y =4 u

Total number of girls
= 4 u + 4 u
= 8 u
= 8 x 6
= 48

Answer(s): 48