Wrong, But Useful: Episode 2


It’s a new month, which means it must be time for a new episode of Wrong, But Useful!

This time around, we talked about queuing at EuroDisney, how to play Battleships, why Peppa Pig’s dad has a quadratic equation in his office, 110%, elliptic curves and Dave’s brilliant new game.


The puzzle:

I have three indistinguishable coins: one always comes up heads, one always comes up tails and the third is a fair coin. I pick one of the coins at random and toss it twice and get the same result both times. What is the probability I picked the fair coin?

What I don’t understand:

Why matrix multiplication works the way it does.


Colin is a Weymouth maths tutor, author of several Maths For Dummies books and A-level maths guides. He started Flying Colours Maths in 2008. He lives with an espresso pot and nothing to prove.


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Where do you teach?

I teach in my home in Abbotsbury Road, Weymouth.

It's a 15-minute walk from Weymouth station, and it's on bus routes 3, 8 and X53. On-road parking is available nearby.

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