Odds of two people's phone numbers both ending in 99?

BobG

New Member
I’m a history major, so I’m hoping a mathematically minded person much smarter than me can help me out.

I believe a single person manages two Twitter accounts that have interacted in the past. The password reset number for both accounts end in 99. One twitter account has 11,400 followers and the other has 3,600.

Im trying to prove the point that the odds of the two following each other, and interacting, and both having account numbers that end in the same two digits, is unlikely.

Can anyone help? Thanks!

Archidamus

Member
First you are going to have to make an assumption that digits are completely random and all have the same chance of occurance. With that in mind, then you can make the claim that the odds of any single person having the last 2 digits of 99 to be 1/100 (10 options for the first digit * 10 options for the next digit = 100). Because all digits are equally likely, you can expand this to say, given person A with 2 digits, the chance of person B having the same digits is 1/100.

Now with that in mind, is 1/100 really that unlikely? There are how many million twitter accounts, and 1% will have the same digits. Just my opinion, I would look for other pieces of evidence to make the case, one way or the other.