Correct Answer - Option 3 : 100
Given,
The students in three classes are in the ratio 2 : 3 : 5
⇒ Let the students in the class be 2x, 3x and 5x respectively
Now,20 students are added to the class and the ratio is 4 ∶ 5 ∶ 7
∴ (2x + 20)/(3x + 20) = 4/5
⇒ 10x + 100 = 12x + 80
⇒ 2x = 20
⇒ x = 10
∴ The total number of students before the increase = (2 + 3 + 5) × 10 = 100
∴ The total number of students before the increase were 100