Hey Hamid, Both sound gramatically correct to me, but I think there's a very slight difference between the two. 1. "I was exhausted at the end of the day." This just sounds like you were tired at the end of the day. 2. "I was exhausted by the end of the day." This sounds like you had a busy day, like helping a friend move or going to classes. Good question! Hope my answer helps a little bit.

Hey I believe that both of them are grammatically correct, but there seems to be a slight difference between them: "I was exhausted at the end of the day" = it means that you felt very tired when the day came to an end (literally at the end of it) "I was exhausted by the end of the day" = it means that something occured throughout your day that made you feel very tired! (You just had a busy day as if you had done lots of stuff!) That's it! Hope I have been of some help to you!

I would use the following sentence- I was exhausted by the end of the day.