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The students in three classes are in the ratio 2 : 3 : 5. If 20 students are increased in each class. The ratio changes to 4 : 5 : 7. The total number of students before the increase were ?
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- 10
- 90
- 100
- None of these
Correct Option: C
Let the number of students be 2x, 3x and 5x
∴ (2x + 20) : (3x + 20) : (5x + 20) = 4 : 5 : 7
⇒ (2x + 20)/4 = (3x + 20)/5 = (5x + 20)/7
⇒ 5(2x + 20) = 4(3x + 20)
∴ x = 10
Hence, total number of student before increase = 10x = 100.
