Correct Answer - Option 4 : 13 minutes
Given
Number of questions solved by Karan in 10 minutes = 20
Number of questions solved by Bhavik in 10 minutes = 50
Calculation
Karan solve questions in 1 minute = 20/10 = 2
Bhavik solve questions in 1 minute = 50/10 = 5
Karan and Bhavik solve questions in 1 minute together = 2 + 5 = 7
91 questions were solved by them in 91/7 = 13 minutes
∴ 91 questions solved by Karan and Bhavik in 13 minutes