英语阅读求救Mr.knight was the manager of a hotel in Springfield.On

英语阅读求救
Mr.knight was the manager of a hotel in Springfield.One weekend all of the hotel were full because of a large business meeting being held in the city.On Sunday night ,three men came into Mr.knight\'s hotel and asked for rooms.Mr.knight told them that there were no rooms available but a very small room as they had no place to stay in.
Mr.knight told them that the room would be $30,$10 for each man.Each man gave him $10,and then they went up to the room.
Mr.knight soon began to think,"Thirty dollars is too much for that small room."He called his assistant over and said :"Here is $5.Give it to the men in the small room.They paid me too much for that room."
The assistant took the money while he was on the way to the small room,he thought :"How can three me divide $5?I\'ll give each of them only $1 and I will keep $2.The men will be happy to get anything back.I will make a little money,and Mr.knight will never know." So the assistant retuned $1 to each of the three men.
Each man had first paid $10.After the assistant returned $1 to him ,each man had actually paid only $9.There were three men .$9*3=$27.The assistant kept $2.$27+$2=$29.where is the missing dollar?
阅读题目最后一题：
Where is the missing dollares?
A,The assistant had it B,There is no misssing dollares.
我感觉是那个assistant私吞2dollars,那么问missing 不就是 The assistant had it
为何选择B呢?数学不好估计俺
Each man had first paid $10.After the assistant returned $1 to him ,each man had actually paid only $9.There were three men .$9*3=$27.The assistant kept $27+$2=$29.where is the missing dollar?

答案应该是选B.
楼主应该看懂了文章和题目了吧.
题中所谓的the missing dollar(应该不是dollars/dollares?),应该是指“三房客最先付得3×10=30美元”和“三房客最终付的房费(10-1)×3 + 2 = 29美元”之间“30-29=1”多出的1美元.
但是事实上三个房客只付了“30-5=25,再加上assustant(助手)私下吞的2美元”,也只有29美元.