There were an equal number of boys in Class V and Class W. ⁴₅ of the pupils in Class V and ¹₄ of the pupils in Class W are girls. If there are 66 more girls in Class V than in Class W, what is the total number of pupils in Class V and Class W?
Fraction of the pupils in Class V that are boys
= 1 - ⁴₅
=  ¹₅

Fraction of the pupils in Class W that are boys
= 1 - ¹₄
= ³₄ 

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

 1x35x3 Class V = 34 Class W 
 315 Class V = 34 Class W

Number of boys in each class = 3 u

Total number of pupils in Class V = 15 u
Total number of pupils in Class W = 4 u

Number of girls in Class V
= 15 u - 3 u
= 12 u

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

Number of more girls in Class V than Class W
= 12 u - 1 u
= 11 u

11 u = 66

1 u = 66 ÷ 11 = 6

Total number of pupils
= 15 u + 4 u
= 19 u
= 19 x 6
= 114

Answer(s): 114