Correct Answer - Option 1 :
\(5\frac{1}{4}\) days
Given
Ravi and Mohan can complete work = 3 days
Ravi alone complete the work = 7 days
Formula Used
Work = time × efficiency
Calculation
⇒ LCM of (3, 7) = 21
⇒ Let the total work be 21
⇒ Efficiency of Ravi and Mohan together = 21/3 = 7
⇒ Efficiency of Ravi alone = 21/7 = 3
⇒ Efficiency of Mohan = 7 - 3 = 4
⇒ Mohan takes time to complete the work alone = 21/4 = \(5\frac{1}{4}\) days