Class 6R and Class 6S have a total of 140 students. ¹₅ of the students in Class 6R and ⁵₉ of the students in Class 6S are girls. The number of boys in Class 6R is equal to the number of boys in Class 6S. Find the total number of boys in the 2 classes.
Fraction of Class 6R that are boys
= 1 - ¹₅ 
= ⁴₅

Fraction of Class 6S that are boys
= 1 - ⁵₉ 
= ⁴₉ 
 
The number of boys in Class 6R is equal to the number of boys in Class 6S.

The numerators are the same.  

⁴₅ Class 6R = ⁴₉ Class 6S 

Number of students in Class 6R = 5 u
Number of students in Class 6S = 9 u

Total number of students 
= 5 u + 9 u
= 14 u

14 u = 140

1 u = 140 ÷ 14 = 10

Number of boys in Class 6R =4 u
Number of boys in Class 6S =4 u

Total number of boys
= 4 u + 4 u
= 8 u
= 8 x 10
= 80

Answer(s): 80