Posted in probability, puzzles.

In a recent MathsJam Shout, courtesy of Bristol MathsJam, we were given a situation, which I paraphrase: Cards bearing the letters A to E are shuffled and placed face-down on the table. You predict which of the cards bears which letter (You make all of your guesses before anything is

Read More →
Posted in probability.

I don't remember doing it - although I'd meant to for some time - but apparently I signed up for the British Bone Marrow Registry. (If you're between 17 and 40, you can sign up the next time you give blood; the more people on the register, the more likely

Read More →
Posted in probability.

It's always Alice and Bob. Why must it always be Alice and Bob? In any case, the two of them are tossing coins Until they hit a particular sequence: Alice until she hits a head then a tail, Bob until he hits two heads in a row. Counter-intuitively, Alice will

Read More →
Posted in probability.

A nice prompt from @shahlock, some time ago: Math Prompt #apstats #mtbosTwo players A, B. A is 4-0 against B. How would you estimate probability A wins next match? Assume independence — M Shah (@shahlock) November 27, 2016 Stand back, everyone: I'm going to apply Bayes's Theorem. A prior Let's

Read More →
Posted in probability, puzzles.

When the redoubtable @cuttheknotmath (Alexander Bogomolny) poses the following question: Two Coins: One Fair, one Biased https://t.co/Rz2zR3LRDj #FigureThat #math #probability pic.twitter.com/HHhnyGjhkq — Alexander Bogomolny (@CutTheKnotMath) March 5, 2018 ... you know there must be Something Up. Surely (the naive reader thinks) the one with two heads out of three is

Read More →
Posted in ninja maths, probability.

A professor - according to Reddit - asked their class how many people you'd need to have in a room to be absolutely certain two of them would have Social Security numbers1 ending in the same four digits (in the same order). 10001, obviously. How about a probability of 99.9%?

Read More →
Posted in probability.

A Christmas Pudding Puzzle I swear, this one came up in real life! My partner made a Christmas pudding for the most recent festive season. Delicious, it was. When it was about half-eaten, I went to microwave a portion. "Hang on," she said: "there might be a coin in there."

Read More →
Posted in probability.

This post is inspired by a Futility Closet article. Do visit them and subscribe to their excellent podcast! Suppose you're dealt a bridge hand1, and someone asks whether you have any aces; you check, and yes! you find an ace. What's the probability you have more than one ace? This

Read More →
Posted in probability, ranting.

In an early draft of my forthcoming book, The Maths Behind, which will be available wherever good books are sold from September, I believe, I took the following unprovoked dig at Australia: "... it crashed into the ocean about 1,600 miles to the west of Perth, Australia. There's nothing there.

Read More →
Posted in probability.

For all the grief I give @reflectivemaths on Wrong, But Useful, he does occasionally ask an interesting question. In episode 45, he wondered how many packs of Lego cards one would need to acquire, on average, to complete the set of 140?1 A simpler case Suppose, instead of 140 cards,

Read More →