On Primality in Packsizes

Oooh la la Mister Maker! Benny George, our precocious two-year-old, is quite the fan of Mister Maker, and enjoys spending time doing arty crafty stuff with his mum. Now, the great thing about the BBC is that they tend to suggest projects which can be created using bits and bobs that you’re likely to have around the home – old cereal boxes and the like. But occasionally some specialist resources have to be procured in the name of Ben’s art, and so it was that Joce today spent £1.99 on a pack of the “googly eyes” so beloved of Maker.

Here’s the thing though – I couldn’t help but noticing that these 20mm googly eyes come in packs of seventeen. Joce charitably suggested that this was simply the number of eyes that could fit in the packet, but I am more cynical. Can it really be a coincidence that eyes – which are surely generally found in pairs – are sold in an odd quantity, forcing the purchaser to buy slightly more than they required?

And we’re not just looking at an odd number here – 17 is prime too, so even if you happened to be creating models of, say, the three-eyed Tuatara lizard, you’re still going to end up with some product left over or feel obliged to buy another pack.

Cunning folk, these googly eye marketers, and it makes me wonder why other manufacturers stick to selling their products in multiples of integers with many divisors. Ease of packaging, perhaps.

What other products are sold in prime quantities?

#1  avatar John Conners on 23 Oct 2009 at 11:03

Heh heh, reminds me of when I was a waiter in my student days. I'd always make sure the petit fours that went out with the coffee meant people would have to fight over one. So if there were 2 people I'd put 3 out, 4 people I'd put out 5 and so forth. Evil you see!

#2 ian avatar Ian Nelson on 23 Oct 2009 at 11:39

You're an evil man Mr Conners. Did any of your customer ever turn the tables and present you with NP-complete problems in the orders, a la this xkcd strip? http://www.xkcd.com/287/

#3  avatar John Conners on 23 Oct 2009 at 11:48

Hahaha! Nobody did but maybe I'll have to try that next time I dine out! ;)

#4  avatar Jeremy Pearson on 24 Oct 2009 at 13:31

So there's more to a baker's dozen than we're led to believe. Thought it seemed too good to be true :(

#5  avatar Nick McMahon on 09 Dec 2009 at 20:46

Maybe I'm under estimating your child, but is it not so that there will be an even number left after he's put one up his nose? Or was he the one to point out the primality?

#6 ian avatar Ian Nelson on 09 Dec 2009 at 22:51

@Nick - Ben says primes are passe, he's only interested in Superior highly composite numbers.

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