还有一元钱去了哪里了？咳咳，偶不说假话，也不说废话，开始正题：有3个人去投宿，一晚30元。三个人每人掏了10元凑够30元交给了老板。后来老板说今天优惠只要25元就够了，拿出5元命令服务生退还给他们，服务生偷偷藏起了2元，然后,把剩下的3元钱分给了那三个人，每人分到1元。

这样，一开始每人掏了10元，现在又退回1元，也就是10-1=9，每人只花了9元钱，3个人每人9元，3× 9 = 27元， 再加上 服务生藏起的2元=29元，还有一元钱去了哪里了？？？有谁知道答案呢?

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