To start off i believe xur and loot drops are npt random. That being said there are problems with your argument. You need to enter higher level stats to learn a few more things but your equations are good. But remember in a random sample which is what you have taken it is just that. A random sample. We have only had so many trials with xur and even if xur had come to the tower we still wouldn't be able to prove randomness or not. Example: If a fair dice is rolled 10 times and all 10 times showed a 1 on the face would you still statistically say its weighted or not a random toss. No. Even of you did 100 trials of the same example you can't prove randomness or weighted values unless you test the whole population of trials which only bungie knows. The math is correct but attempting to prove that from a random sample of just a few weeks of samples you can prove something is statistically biased is not only wrong but mathematically impossible. But as I said at the beginning I do accept that even though there can be no proof of a weighted mood drop or xur table I do believe there is. Regards Grad student in Statistics