数学题：假设有一个池塘，里面有无穷多的水。现有2个空水壶，容积分别为5升和6升。问题是：如何只用这2个水壶从池塘里取得3升的水。

数学题解答：

先装满5升的水壶，然后倒到6升水壶里，再装满5升水壶，再往6升水壶倒满，这样5升水壶就剩下四升水。

然后把6升水壶里的水倒掉，把5升水壶里的四升水倒进6升水壶里，然后再装满5升水壶，再倒入6升水壶。

这样因为6升水壶原先有四升水，现在就只能倒入2升。那5升水壶就只剩下3升水了。

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