Therefore, you may calculate the probability of neither of the 2 gold coins being on the tiles.
Then use the fact that all probabilities sum to 1.
The only possibilities are
(1) no coins
(2) 1 coin (either one)
(2) 2 coins.
Your required probability is (1) or (2) for which we'd sum the probabilities.
You could calculate those.
However, instead you can calculate the probability of (1) and subtract the answer from 1.
Hence, begin with the probability of the first tile not containing a coin is 23/25, the 2nd not containing a coin is 22/24 etc.