A, B and C can complete a piece of work in 6, 8 and 15 days. C alone works for 5 days and then quit . After that in how many days work is completed by A alone ?

4

Total work = Efficiency × Number of days

work done by C = 8 × 5 = 40 

remaining work = 120 - 40  = 80

so time taken by A to finish the remaining work

= \(\frac{80}{20}\) = 4 days