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A-level probability question, to bring joy to children at Christmas:… - Sally's Journal
November 19th, 2013
12:01 pm

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From:atreic
Date:November 19th, 2013 01:44 pm (UTC)
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OK, it turns out you can do this in an excel spreadsheet (you just calculate P(1,0) and P(1,1) and then stick in the formula for the recursion.

P(10,5) is a miserable 16% (although you'll have a 44% chance of having that oh-so-frustrating 4)

To actually get P(N,5) > 0.90, you need to order 30 Octonauts.

On the other hand, a pile of 30 Octonauts would be great :-)
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From:cartesiandaemon
Date:November 19th, 2013 02:45 pm (UTC)
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I guess it depends what happens to the surplus. Do they just get returned to the warehouse? Or do they assemble into one giant robot Octonaut that saves the planet!?
From:sain_bano
Date:November 19th, 2013 02:51 pm (UTC)
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You are fabulous! (and I'm quite pleased that this turned out to be a not trivially easy problem, rather than just that my brain has turned to complete mush after having children, though I was never very good at thinking in the right way for probability questions)

I couldn't quite bring myself to order in 30 sets of figures, so have ordered 10 and will report back on Thursday when I pick them up about what I ended up with. My disappointment at the dismal success rate predicted is improved slightly by the thought that once I've bought the figures at offer price, I can then order more in if needed and exchange even after the offer has finished. I'm sure all this would be easier if any of the Tescos in a 20 mile radius actually stocked the darned things.
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From:atreic
Date:November 19th, 2013 02:58 pm (UTC)
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On the bright side, if you do get the five you want, you can feel very smug about not only have the five you want, but also about knowing how lucky you were to manage it! :-)

We have a big tescos with lots of toys that is our local, so if you do end up trying to hunt down Just One, let me know... I haven't specifically looked for Octonauts though.
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