Say I had 400 tiles (20 x 20) and 50 objects. If I put these objects RANDOMLY on the 20x20 tiles. What is the chance that I have atleast 2 objects that are placed on the same tile?

What I did was in a double for loop, I counted the amount of random generated objects. If I got an amount of 2 duplicates, I would divide this by 400 and then multiply it by 100 so I would get for example here: 0.5%.

Is this correct?