I asked a question on MO and it now has three correct answers, all more or less using the same strategy and similar to each other. If I accept all of them, do they all get the reputation they deserve?
As others have stated, you cannot accept more than one answer.
Don't worry about reputation too much, I think almost no one cares if they get 15 points more or 15 points less than others.
Accept the answer you like most, and if they all look the same to you go by some arbitrary rule to break ties like the chronologically first answer, the answer with highest vote, etc.
In absence of good reasons to prefer one answer, sometimes people choose the first given one, and leaves some nice comment to the others.
(Look e.g. here: I was honored to have the same example as George Lowther, even with the same notation, one minute later).
Since you can't accept more than one answer, a common method to approximate fairness is to accept one, and vote up the other correct answers. One person will get 5 more points than the others.