Prince hires three persons A, B and C for a piece of work. A can do 2/5th the work in 12 days, B can do 3/5th of the same work in 15 days. A and B started the work together but after 10 days both left the work. After that C alone complete the remaining work in 4 days. Then find in how many days all three together can complete 28% of the same work?

A does 2/5 work in 12 days, so A's rate = (2/5)/12 = 1/30 per day. B does 3/5 work in 15 days, so B's rate = (3/5)/15 = 1/25 per day. A and B together for 10 days complete 10(1/30 + 1/25) = 10(11/150) = 11/15 of work. Remaining work = 1 - 11/15 = 4/15. C completes 4/15 in 4 days, so C's rate = (4/15)/4 = 1/15 per day. Combined rate of A, B, C = 1/30 + 1/25 + 1/15 = (5 + 6 + 10)/150 = 21/150 = 7/50 per day. For 28% = 28/100 = 7/25 of work: Time = (7/25)/(7/50) = 2 days.