There were an equal number of boys in Class A and Class B. ⁵₆ of the pupils in Class A and ¹₆ of the pupils in Class B are girls. If there are 144 more girls in Class A than in Class B, what is the total number of pupils in Class A and Class B?
Fraction of the pupils in Class A that are boys
= 1 - ⁵₆
=  ¹₆

Fraction of the pupils in Class B that are boys
= 1 - ¹₆
= ⁵₆ 

The number of boys in Class A is equal to the number of boys in Class B. LCM of 1 and 5 is 5. Make the numerators the same. 

 1x56x5 Class A = 56 Class B 
 530 Class A = 56 Class B

Number of boys in each class = 5 u

Total number of pupils in Class A = 30 u
Total number of pupils in Class B = 6 u

Number of girls in Class A
= 30 u - 5 u
= 25 u

Number of girls in Class B
= 6 u - 5 u
= 1 u

Number of more girls in Class A than Class B
= 25 u - 1 u
= 24 u

24 u = 144

1 u = 144 ÷ 24 = 6

Total number of pupils
= 30 u + 6 u
= 36 u
= 36 x 6
= 216

Answer(s): 216