There were an equal number of boys in Class Y and Class Z. ⁵₆ of the students in Class Y and ¹₄ of the students in Class Z are girls. If there are 84 more girls in Class Y than in Class Z, what is the total number of students in Class Y and Class Z?
Fraction of the students in Class Y that are boys
= 1 - ⁵₆
=  ¹₆

Fraction of the students in Class Z that are boys
= 1 - ¹₄
= ³₄ 

The number of boys in Class Y is equal to the number of boys in Class Z. LCM of 1 and 3 is 3. Make the numerators the same. 

 1x36x3 Class Y = 34 Class Z 
 318 Class Y = 34 Class Z

Number of boys in each class = 3 u

Total number of students in Class Y = 18 u
Total number of students in Class Z = 4 u

Number of girls in Class Y
= 18 u - 3 u
= 15 u

Number of girls in Class Z
= 4 u - 3 u
= 1 u

Number of more girls in Class Y than Class Z
= 15 u - 1 u
= 14 u

14 u = 84

1 u = 84 ÷ 14 = 6

Total number of students
= 18 u + 4 u
= 22 u
= 22 x 6
= 132

Answer(s): 132