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**