Arshi can do a piece of work in 30 days, while Ahan can complete it in 20 days. Both together labour for 4 days and afterwards Ahan leaves. How long will Arshi take to complete the remaining work?

20 days

Arshi = 30 days, Ahan = 20 days,

⇒ They both worked for 4 days and the Ahan left = (2 + 3) x 4 = 5 x 4 = 20 units,     ..(Efficiency × Days = Work)

⇒ Remaining work = 60 - 20 = 40 units,

⇒ Time required by Arshi to complete the remaining work alone = \(\frac{40}{2}\) = 20 days,     ..(\(\frac{Work}{Efficiency}\) = Time)