6th Grade Working/Engineering Problems: Problem 3

Problem: The hoses 1, 2, 3, all spray water into a pool. If only hoses 1 and 2 are opened, it takes 5 hours to fill in the entire pool; If only hoses 2 and 3 are opened, it takes 4 hours to fill in the entire pool. If hose 2 is opened for 6 hours and then closed, and hoses 1 and 3 are opened at the same time, it takes them 2 hours to fill in the entire pool. How many hours does it take for hose 2 itself to fill the entire pool?

Key: Eliminate variables, set 'unit 1' value

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