There were an equal number of boys in Class J and Class K. ⁴₅ of the students in Class J and ¹₆ of the students in Class K are girls. If there are 190 more girls in Class J than in Class K, what is the total number of students in Class J and Class K?
Fraction of the students in Class J that are boys
= 1 - ⁴₅
=  ¹₅

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

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

 1x55x5 Class J = 56 Class K 
 525 Class J = 56 Class K

Number of boys in each class = 5 u

Total number of students in Class J = 25 u
Total number of students in Class K = 6 u

Number of girls in Class J
= 25 u - 5 u
= 20 u

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

Number of more girls in Class J than Class K
= 20 u - 1 u
= 19 u

19 u = 190

1 u = 190 ÷ 19 = 10

Total number of students
= 25 u + 6 u
= 31 u
= 31 x 10
= 310

Answer(s): 310