Correct Answer - Option 2 : 20 days
Given
Karan and Arjun together completes a work in 7.5 hours
Arjun alone completes a work in 12 days
Calculation
Let y days will be required by Karan to complete a work
Work done in one day by Arjun and Karan = (1/7.5)
Work done in one day by Arjun = (1/12)
Work done in one day by Karan = (1/y)
(1/12) + (1/y) = (1/7.5)
⇒ (1/y) = (1/7.5) - (1/12)
⇒ (1/y) = (40 - 25)/300
⇒ 1/y = 15/300
⇒ y = 20
∴ Karan can complete a work in 20 days.
