有3个人去开房间100块1间后来老板说全部优惠50可小工自己拿起了20就是说一人现在用了290可小工拿了20到那

最早接触到同类型题是在高中英语资料上，后来就看到不少类似版本。
英文版：
Q:
Three men eat at a restaurant. The bill comes to £25. They each pay £10. When the waiter brings the £5 change
they each take back £1 each and leave a £2 tip. So each man has paid £9, which totals £27. The waiter has the £2 tip, which makes £29, so where's the other £1 gone?
A:
3 men paid £9 each which came to £27.
The waiter's £2 tip came from this £27 and not in addition to to the £27.
Each man paid £10 and took his £1 change back.

In other words, the cost of the meal plus the tip came to £27. This was paid by each man paying £9 (£10 minus the £1 change).
常见的是这样，当然也有用你说的住宿做例子的。

有3人去投宿,一晚30元.三个人每人掏了10元凑够三十元交给了老板.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 X 9 = 2 7 元 +