Suspicious Behaviour Equals 0.000125


And just like that, thanks to @jsprty on The Twitter (or Jasper if you are lucky enough to know him IRLin real life), we are at the airport. In fact, we’ve managed to successfully navigate the labyrinth of the airport. Which isn’t really so much a labyrinth as it is a set of lines connecting one security check point with another security check point. But I digress.

Anyway, the first security checkpoint is where my adventure begins. On arrival, security officer Phil (his name I don’t actually remember, but for the sake of this story we’ll call him Phil) was deep in conversation with security officer Colin (I didn’t catch his name either). They were chatting about a previous passenger, who was apparently on the larger side of heavy. She was also only 17, or so she claimed. And, for my benefit (according to Phil), she was also rather well endowed for a girl of her young years. So much so, that Phil didn’t believe she was 17.

Following this conversation, he then informed me that sometimes he likes to look at breasts to ‘test’ the ages that are claimed on passports. I’m really not sure I believed him. He did inform me that ‘checking me out’ was easy. I really didn’t know how to respond to that. I think at that point he realized that he had a job to do, and proceeded to ask me why I was travelling, where I was going, etc. The usual list of questions. He also, as often is the case, asked about my profession.

“I’m an Assistant Professor.”

“What do you teach?” he queried.

“Statistics.” I like to keep my answers short and to the point.

“Alright then. Given that there are 20 security agents working right now, what is the probability that you randomly were assigned to me?”

Seriously. He asked me that.

My first reaction was to chuckle. Then, being the nerd that I am, I started to ponder how I arrived at Phil’s security station (clearly it depended on the length of the queue before me, the wait times at each agent, directions from the guy sending people to the sub-queues, etc.). None of this was relayed to Phil, of course. In fact, it all happened in a flash in my head so I didn’t even skip a beat when I replied


“Good. Good. Now, if you were to come back tomorrow, what is the probability that you’d come through my gate again? That is, what is the probability that you’d see me two days in a row?”

“If I am to assume that all of you are working tomorrow, and the assignment of passenger to security checkpoint is completely random and independent, then 1/20 times 1/20, so 1/400.”

“What about 3 days in a row?”

“1/400 by 1/20.”

“Excellent. So basically, if I am to see you pass through my security check point more than twice, I’m going to consider that behaviour very suspicious.”

I couldn’t help but smile and laugh.

Phil, you made my day. Thanks.


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