1. The letter on the table is yours.

Question

2. A letter on the table is yours. Find it.
[#1 is correct, isn't it? What about #2? If there are three letters, and one of them is yours, then can we use #2?]

Answer 1

yes, yes, sure you may

Answer 2

by the way
'You may do it' means you are allowed to do it. (no law against it)
'You can do it' means you are able to do it. (strong enough for example)