Question

1. I was poor in the past.
2. I am not so rich in the present/at present.
3. I will be rich in the future.
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Are they all grammatical? Can we use both 'in the present' and 'at present'? How about 'at the present'? Which one is commonly used?

Answer 1

All are fine, yes.

And, yes, you can use any of those three phrases in #2. They're all fairly commonly used, although "at present" is probably most common.

Answer 2

Thank you for your help.
What about 'at the present'?

Answer 3

"at the present" or "at present" -- both mean the same thing. But "at present" is the more commonly used between these two.