A, B and C can do a piece of work in 10 days, 12 days and 15 days respectively. They work together after 2 day A left the work and after 2 day B also left. Find in how many days the total work will complete?

Work rates: A=1/10, B=1/12, C=1/15 per day. Days 1-2: All work together. Rate = 1/10+1/12+1/15 = 6/60+5/60+4/60 = 15/60 = 1/4. Work done = 2×(1/4) = 1/2. Days 3-4: B and C work. Rate = 1/12+1/15 = 5/60+4/60 = 9/60 = 3/20. Work done = 2×(3/20) = 3/10. Total done = 1/2+3/10 = 8/10 = 4/5. Remaining = 1/5, C does it alone in (1/5)/(1/15) = 3 days. Total = 4+3 = 7 days.