To put it bluntly, the chance for a Gorgon is 10% (9%), and for 10 Gorgons, the chance is 90% (approximately).
For 10 Gorgons, the chance is not 90%, but 1 - 0.9^10 = 65%.
Each Gorgon has its own separate probability. I don't know how else to explain it; people just don't understand... maybe you should study higher mathematics. Read a few pages of the discussion carefully.
