Who doesn’t like birthday cakes? And what I’m going to show you today is that there are good ways and there are bad ways of cutting a cake. And the classic way,
the bad way, is like this,
which would be normal. You put the knife in the center. One bit of a slice, Other bit of a slice…
[laughter]Brady Haran: It’s like the classic.
Alex Bellos: It is the classic. Isn’t it?
It’s almost like a pie chart. You know, one thing about
the word pie chart. In France they call them Camembert,
which is like a cheese. It’s actually like a cheese chart in France. Interesting cultural differences
in math speak. So this is what you would do.
You take this, you would put this over here, you eat it, and then you leave
this in the fridge overnight. And the reason why
this is a really bad way of cutting a cake is that these bits here
are just going to get dry. So when you come the following day
to have your cake, you know, you do another one, another slice like this This side here, hmm, lovely and soft This will be dry and horrible. You know, maximizing the amount
of gastronomic pleasure that you can make out of this cake. There is a better way,
a way that is more than a hundred years old and was discovered or invented by one of Britain’s most famous and
brilliant mathematical scientists. This is a copy of Nature,
the famous science magazine, from December the 20th 1906. And in the Letters To The Editor here
it says: The headline: Cutting a round cake
on scientific principles. “The ordinary method of cutting out
a wedge”, he writes, “is very faulty”. What he suggests is,
and he gives an illustration for it, The proper way,
the scientific way, the mathematically perfect way of
cutting a round cake and it is as follows. So we have another cake The first slice will be like this. Breaking all the rules
of a cake etiquette. Perfect. OK?
So this is the first one, and then I need to find a way of… taking it out… OK. We can stick that there. And that is got to be the prime steak
of that cake. Isn’t it? It’s the T-bone cut. Here’s what we need to do… We need to close the cake together,
like this. And it’s going to come apart,
so look what I’ve got here… I have got some rubber bands
to make sure it stays together. The following day… All the flesh, the sponge
is going to be nice and soft. So, how do we do the second slice? The second slice…
I guess it’s not your birthday anymore, so you’re not going to have one
quite as big… It will be interesting to work out
the actual proportions. This is… You get a lovely break in the elastic
bands too, which is exciting. This is slice two. Or, it actually is slice two
which has two slices, two parts. So you put this back together.
And we can keep on going. Obviously, I’m going to want to use
the elastic band to put the cake… Yeah, That is perfect. That is going to stay
so fresh for day three. Day three.
Brady Haran: Actually do day three, Gab. Alex Bellos: Let’s turn it around. I think this is going to be the slice
for day three. Again, the satisfying snap of
the elastic bands… And… I don’t know if you thought
about if before, but these triangular slices are really
annoying anyway, because… It’s not very satisfying. Having a nice
uniform slice like that is a lot better. So, here we go again… At the end of day three… This is for…
And this is going to be perfect. And gradually we are slicing it,
keep on going. I think for the mathematical loners who don’t want to share their cakes
it could be useful. Brady Haran:
For a bit more of this interview including more about the guy
that came up with this cake cutting method have a look at the extra footage
over Numberphile 2. And if you just like to hear more
great stories from Alex, he’s got a new book out
just recently: “Alex through the Looking Glass – How Life Reflects Numbers
and Numbers Reflect Life”. It’s really good.
It’s also just out in the US, but it has a different name in the US. It’s called “The Grapes of Math”. I’ll put links to it
in the video description.