Question

The students in three classes are in the ratio of 2 : 3 : 4. If 40 students are added in each class, the ratio becomes 4 : 5 : 6. Find the total number of students in all the three classes is :

Answer 1

Let the number of students be x
number of students in 1st class = 2x
number of students in 2nd class = 3x
number of students in 3rd class = 4x
after adding 40 students to each class ,
number of students in 1st class = 2x+40
number of students in 2nd class = 3x+40
number of students in 3rd class = 4x+40
according to question,
2x+40+ 3x+40+4x+40= 4x+5x+6x
= 9x+120= 15x
120 = 15x-9x
120= 6x
x= 120/6= 20
there total number of students in all the classes = 2*20 +3*20+4*20
= 40+60+80 = 180
after adding 40 students to each class , total number of students in all the class = 120 +180 =300.

Answer 2

difference bitween 2x:3x:4x and 4x:5x:6x = 2x
2x= 40
then x= 20
total num of student= 4x+5x+6x=15x 
put the value of x=20 then total student =300