fun little trivia fact i discovered while talking to alex crunchlax last night
if you give someone the 7 digits of your phone number, but not the area code or the order in which the digits go in. that person has a one in five million chance of calling your phone number.
area codes are three digits long and assuming all area codes from 000 to 999 are valid that leaves 1000 possible area codes to try.
the chances of ordering 7 digits correctly is given by 7! which is 7*6*5*4*3*2*1 or 5040. Roughly 5000.
For each of those 5000 phone numbers they try, they must also try 1000 area codes, therefore the probability of getting the full complete phone number would be 1 in 1000*7! or about 1000*5000 which is 5 million.
for example, if the guesser was able to narrow down the area code to three possibilities the probability that they’d guess your full phone number would be 1 in 3*5000 or 15,000
