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Here is my new logic puzzle.
I thought of a positive integer that is below 100 and is divisible by 7. In addition to the public knowledge above, I privately tell the units digit of my number to Alice and the tens digit to Bob. Alice and Bob are very logical people, but their conversation might seem strange:

Alice: You do not know Tanya’s number.
Bob: I know Tanya’s number.

What is my number?
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Please comment.

Your answer,  not entirely wrong, should be expanded. 

Is there an answer to Tanya's question?

Only one possibility or more?

Are A and B very logical people?