There were an equal number of boys in Class N and Class P. ³₄ of the students in Class N and ¹₆ of the students in Class P are girls. If there are 140 more girls in Class N than in Class P, what is the total number of students in Class N and Class P?
Fraction of the students in Class N that are boys
= 1 - ³₄
=  ¹₄

Fraction of the students in Class P that are boys
= 1 - ¹₆
= ⁵₆ 

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

 1x54x5 Class N = 56 Class P 
 520 Class N = 56 Class P

Number of boys in each class = 5 u

Total number of students in Class N = 20 u
Total number of students in Class P = 6 u

Number of girls in Class N
= 20 u - 5 u
= 15 u

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

Number of more girls in Class N than Class P
= 15 u - 1 u
= 14 u

14 u = 140

1 u = 140 ÷ 14 = 10

Total number of students
= 20 u + 6 u
= 26 u
= 26 x 10
= 260

Answer(s): 260