Class 3Y and Class 3Z have a total of 136 students. ¹₆ of the students in Class 3Y and ⁶₁₁ of the students in Class 3Z are boys. The number of girls in Class 3Y is equal to the number of girls in Class 3Z. Find the total number of girls in the 2 classes.
Fraction of Class 3Y that are girls
= 1 - ¹₆ 
= ⁵₆

Fraction of Class 3Z that are girls
= 1 - ⁶₁₁ 
= ⁵₁₁ 
 
The number of girls in Class 3Y is equal to the number of girls in Class 3Z.

The numerators are the same.  

⁵₆ Class 3Y = ⁵₁₁ Class 3Z 

Number of students in Class 3Y = 6 u
Number of students in Class 3Z = 11 u

Total number of students 
= 6 u + 11 u
= 17 u

17 u = 136

1 u = 136 ÷ 17 = 8

Number of girls in Class 3Y =5 u
Number of girls in Class 3Z =5 u

Total number of girls
= 5 u + 5 u
= 10 u
= 10 x 8
= 80

Answer(s): 80