A neat probability rule-of-thumb

Disclaimer: I am NOT a probabilist. Not only have I never taught probability, the last time I took a course in probability was in my sophomore year of college. So if this is well known (or totally wrong), forgive me. A non-mathematician friend of mine shared this link with me. It compares the lifetime risk of dying by various…

The left-handed boy problem

A few months ago Gary Foshee was scheduled to speak at the Gathering for Gardner. He got up and gave a presentation that was all of three sentences. He said: I have two children. One is a boy born on a Tuesday. What is the probability I have two boys? This deceptively simple problem quickly made…

A card trick that will probably amaze your friends (solution)

Warning! Spoiler alert! This post contains the secret behind the card trick that I described in my last post. Read that post before reading this one. First the bad news: this card trick is not fool-proof; it is a probabilistic card trick. The good news is that in my experience, it has a high probability…

Playing the probabilities in Settlers of Catan

One of my favorite board games is Settlers of Catan. I encourage all of you to check it out. It is a great game because it is a combination of luck and strategy and it is different each time you play. I’ve been on a big Settlers kick lately, because I’ve downloaded a version for…

The importance of definitions: chance of rain

Tomorrow’s weather forecast for Carlisle, PA, is: Windy with showers. High 58F. Winds SW at 20 to 30 mph. Chance of rain 40%. First of all, 58 degrees on December 28? Sweet! But what does “chance of rain 40%” mean? Does it mean that there is a 40% chance that it will rain at my…

Four shuffles suffice

It takes a while to shuffle a deck of cards seven times, but it is well known that that is how many riffle shuffles it takes to fully randomize a deck of 52 standard playing cards. This was shown in 1992 by Bayer and Diaconis. As it turns out, however, for some games fewer than…