Zippy coincidence
Posted on:: December 7th, 2004
Mark “Too Much Time on His Hands” Dionne writes, with reference to the zip code map:
Once upon a time my zip code and my social security number both started with the same three digits.
How many people have exactly the same SS number and (nine digit) zip?
I’m no mathematician — as I’m about to prove — but aren’t the odds of having them match 1 in 999,999,999? With a US population of 300,000,000, wouldn’t the odds of there being a current match be about 0.3?
Now, since I’ve never gotten a fact or a simple mathematical equation right, please enjoy yourself explaining how wrong I’ve gone. It’s on me!
Categories: Uncategorized dw
I pulled a dollar bill out of my pocket and the serial number was the phone number of our dog sitter followed by the number of children I have. What are the odds!?
Just to checkpoint this, I pulled a five dollar bill out of my pocket. The serial number was the 2 digit year I graduated from high school followed by the 4 digit year I’ll be 100 followed by the year I wish I’d stopped aging. This is amazing!
I’m guessing that if I keep reading serial numbers on bills I’ll eventually find one that’s perfectly meaningless. No, maybe not. What would be the odds of that?
SSNs are generated from the pool of available numbers based on a person’s place of birth. (I don’t know what the formula is, but for example, both my wife and I were born in the Los Angeles area, and both of our SSN’s start with 5. All zip codes in L.A. begin with 9.)
Statistically, that poisons the randomness of the basic question. A large number of people in one area may have a match with their zip codes, while none in other areas will have a match, unless people move there.