[EVa5I7bHFq9mnYK]

If the percentage of noisy apartments were 90%, the probability of me randomly landing in 6 quiet apartments out of 6 would be 0.1^6, or one in a million. If the percentage of noisy apartments was 10%, that probability would be 0.9^6 = 0.53. So, given my experience, the latter case is 0.53 / 0.000001 = 530,000 times more probable.

[pandaman]

"conditional probability" is the concept you might find enlightening.

[EVa5I7bHFq9mnYK]

You may start with "How Many Jelly Beans?: A Giant Book of Giant Numbers" by Andrea Menotti.