Iam a # that rounds to 40. one of my digits is 3. what # am i? could i be a different number? explain your thinking.

Well the number you could be are 35, 36,37,38, 39,41,42,43. You are correct about one of the digits being 3. 

Well, if your # round's to 40 then your number is either, 35,36,37,38,39,43.
Yes, you could be a different number you could be 6 different numbers. I'm thinking you could be some where in the middle of 35,36,37,38,39,43. ( If you are asking your self why is 43 in this, this is because 43 round's to 40. I would have gone all the way to 45 but I remembered that you stated that the # has a 3 in it)

So your answer is, 35,36,37,38,39,43. (It could be any number in that line)

Good luck on your home work!
Hope this help's!