1. He read the book in 5 days.
2. He read the book after 5 days.
3. He read the book within 5 days.
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In a dictionary, I found that 'in' is used as 'within' in American English. Then it's confusing. Does #1 mean #3 in American English? I think #1 mean that it took 5 day for him to read this book. Am I right? In #3, He may have finished reading the book within 2 days, 3 days, 4 days or 5 days,right? Would you answer the qeustions?
Yes, 1 and 3 mean the same. 3 could mean less than 5 days.
2 means something entirely different.
Thank you. Then, when it took nearly 5 days to finish reading the book, what expression do we have to use?
"when it took nearly 5 days to finish reading the book" -- Then I'd use 3.
Yes, you are correct in your understanding of the sentences. Let me explain them further:
1. "He read the book in 5 days." This means that it took him a total of 5 days to finish reading the book. It does not specify if he finished it earlier or later within those 5 days.
2. "He read the book after 5 days." This sentence suggests that there was a 5-day period of time before he started reading the book. It does not mention how long it actually took him to read the book.
3. "He read the book within 5 days." This sentence implies that he completed reading the book in a period of time that is equal to or less than 5 days. It does not specify if he finished it earlier or later within that time frame. So, you are right that he may have finished reading the book in 2, 3, 4, or exactly 5 days.
Regarding the usage of "in" and "within" in American English, it's important to note that context plays a significant role in determining the intended meaning. While "in" can sometimes be used to mean "within" in certain situations, it is more commonly used to refer to a specific period of time within which an action is completed. It is always a good idea to consider the context and additional information provided to fully understand the intended meaning.