The water inlet pipe is one hour 1/3 and the water outlet pipe is one hour 1/5.

Open the inlet and outlet pipes for 2 hours at the same time, and the total water inflow is (1/3- 1/5)×2.

The time required to fill the whole pool is (1-(1/3-1/5) × 2) ÷1/3 = 2.2 (hours).

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