If i choose 20 cell phone numbers randomly in a population of 37 100 000 cell phone subscribers, how large is the probability that at least two of them during two days in a row (a 48 hour period) will make a call to another person in this group of 20? The actual case involve a call and then an immeditate call back, which should mean that the two subscribers know each other: So the question can maybe be reformulated: How large is the probability in a population ot 37 100 000 that two persons in a random sample of 20 drawn from the 37 100 000 know each other