A can complete a project in 2 months, B can complete the same in 1 month and C can complete it in 20 days. All of them started working together. After five days, A left the project. How many more days are needed to complete the project?

Convert all completion times to days: A takes 60 days, B takes 30 days, and C takes 20 days. Their combined one-day work rate is 1 over 60 plus 1 over 30 plus 1 over 20, which equals 6 over 60 or 1 over 10. In 5 days of working together, they completed 5 times 1 over 10, which is 1 over 2 of the project. The remaining 1 over 2 of the project is completed by B and C at a combined rate of 1 over 30 plus 1 over 20, equaling 1 over 12 per day. Dividing the remaining 1 over 2 by their rate of 1 over 12 shows they need 6 more days to finish the project.

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