There were an equal number of girls in Class V and Class W. ⁵₆ of the students in Class V and ¹₄ of the students in Class W are boys. If there are 42 more boys in Class V than in Class W, what is the total number of students in Class V and Class W?
Fraction of the students in Class V that are girls
= 1 - ⁵₆
=  ¹₆

Fraction of the students in Class W that are girls
= 1 - ¹₄
= ³₄ 

The number of girls in Class V is equal to the number of girls in Class W. LCM of 1 and 3 is 3. Make the numerators the same. 

 1x36x3 Class V = 34 Class W 
 318 Class V = 34 Class W

Number of girls in each class = 3 u

Total number of students in Class V = 18 u
Total number of students in Class W = 4 u

Number of boys in Class V
= 18 u - 3 u
= 15 u

Number of boys in Class W
= 4 u - 3 u
= 1 u

Number of more boys in Class V than Class W
= 15 u - 1 u
= 14 u

14 u = 42

1 u = 42 ÷ 14 = 3

Total number of students
= 18 u + 4 u
= 22 u
= 22 x 3
= 66

Answer(s): 66