Let the number of days taken by Rohit be x. Since efficiency is inversely proportional to the time taken. ⇒ Number of days taken by Mohit = x/5 According to the question, ⇒ x – x/5 = 28 ⇒ 4x/5 = 28 ⇒ x = 35 days Alternate Solution: Let the efficiency of Rohit be 1. ⇒ Mohit’s efficiency = 5 Let Rohit can complete the work in x days. ⇒ Mohit’s efficiency × time = Rohit’s efficiency × time ⇒ 5 × (x – 28) = 1 × x ⇒ 4x = 5 × 28 ⇒ x = 35 ⇒ Total work = Rohit’s efficiency × time = 1 × x = 35 ⇒ Rohit alone complete the work = Total work/ Rohit’s efficiency = 35 days ∴ Rohit alone complete the work in 35 days.