From Dark and Darker Wiki
Yeah unfortunately your math is wrong. The way statics works doesn't follow your thought process.
If the chance of obtaining a Gold Coin Chest is .1%, and you can hit a pile 3-10 times, each time you hit the pile, the probability of getting a Gold Coin Chest remains at .1%.
However, with ten chances, overall, the odds go up to 0.996% in comparison to if someone only hit the pile once.
In layman's terms, every time you hit the pile, you're only going to get a chest .1% of the time. But the more you hit the pile, the more likely it is that you get a chest.
I must note: if a drop is .1%, and you do X to roll of the chance of obtaining the drop 1000 times, you are not guaranteed the drop.