Solution to: Three Taps
The smallest tap fills 1/20 water-cask in 1 minute. The middle tap fills 1/12 water-cask in 1 minute. The largest tap fills 1/5 water-cask in 1 minute.
Together they fill 1/20 + 1/12 + 1/5 = 1/3 water-cask in 1 minute. Therefore, the whole water-cask is filled in 3 minutes.
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