What matters is that only 20 of the total are facing silver side up.

最重要的是全部钱币中有20枚是银面向上的。

And all you have to do is separate them into two piles so that each has the same number of coins facing silver side up.

你只需要把它们分为两堆以让每一堆中银面向上的都有相同的数目。

If it's not facing silver side up, it must be gold side up, and vice versa, and in any combination of 20 coins, the number of gold-facing and silver-facing coins must add up to 20.

如果不是银面向上，那肯定就是金面向上，反过来也一样，任何20枚钱币的组合，金面向上和银面向上的总和一定要等于20.