Two taps fill a tank in 20 and 30 minutes. They are run alternately, each for 2 minutes at a time, starting with the faster tap. How long does the empty tank take to fill?

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Accepted Answer

24 min. In 60ths: faster tap 3/min, slower 2/min. A 4-minute round gives 6+4=10. After 5 rounds (20 min): 50; faster tap 2 min: 56; slower tap needs 4, i.e. 2 min. Total 24 min. (12 min is both open together.)

Two taps fill a tank in 20 and 30 minutes. They are run alternately, each for 2 minutes at a time, starting with the faster tap. How long does the empty tank take to fill?

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