Class 3P and Class 3Q have a total of 85 students. ¹₆ of the students in Class 3P and ⁶₁₁ of the students in Class 3Q are boys. The number of girls in Class 3P is equal to the number of girls in Class 3Q. Find the total number of girls in the 2 classes.
Fraction of Class 3P that are girls
= 1 - ¹₆ 
= ⁵₆

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

The numerators are the same.  

⁵₆ Class 3P = ⁵₁₁ Class 3Q 

Number of students in Class 3P = 6 u
Number of students in Class 3Q = 11 u

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

17 u = 85

1 u = 85 ÷ 17 = 5

Number of girls in Class 3P =5 u
Number of girls in Class 3Q =5 u

Total number of girls
= 5 u + 5 u
= 10 u
= 10 x 5
= 50

Answer(s): 50