Hello Javi, The first one is correct. (It will take at least 20 hours.) But, as mentioned above...You could say number 3. It will take 20 hours, at least. OR It will take 20 hours...at least. The idea here in the third version is that "at least" coming at the end is more of an after thought. Like they are kind of "ball parking" (guessing) how long it will take. The first one is more defined and set in terms of the calculated time it will take to complete. I hope that helps. Happy learning.

It will take at least 20 hours :)

Short version: the first is correct, and so is the last, with a comma before "at least". All can be used in informal speech Long Answer: At least is almost always a phrasal adverb, depending on its usage-- (phrasal just means that it is made up of two separate words) This will sound strange to you, but to a native English speaker, every single one of those sentences is completely correct. Especially while speaking, any of these are used. However, if you want to be careful while writing, or speaking formally, you could use: It will take at least 20 hours It will take 20 hours, at least (I wouldn't worry because "at least" is not generally a phrase used in formal writing)

LOL! sorry! "It will take at least 20 hours." I somehow misread the sentences.