Hello and welcome to more or less on the BBC World Service. We're your weekly guide

to the numbers all around us in the news and in life, and I'm Tim Haafard. This week

a simple number, a number of holes in a regular drinking straw. An easy question to answer

right? Except that you and the person next to you might have a very different view on

what the obvious answer is. This is one of the questions posed by Jordan

Ellenburg, a professor of mathematics at the University of Wisconsin at Madison in

his new book, Shape. I've been talking to him about his aim to help us understand

everything from the pandemic to predicting elections using geometry. And he started by helping

me with that straw conundrum. Really interesting mathematical question

there. What is a hole? Is there a definition that makes sense? So look, to cut to the chase,

there's two main answers people give. People say there's one hole and it goes all the way

through, or they say there's two holes, the hole at the top and the hole at the bottom.

Which one of those is right? Well, that's a long story. And to get there, you have to really

understand all the work that geometries and topologists have done over the years to sort

of try to get at some mathematical notion of what a hole is that actually works.

Well, the thing that really blew my mind about this is when I encountered it, I thought,

oh, come on, there's obviously just one hole. You know, you could hold up the straw, you

look through, there's the hole. What's the question? Then you started talking about trousers

or you called them pants, but I'll forgive you for that. And well, how many holes in

a pair of trousers? Well, obviously three, you know, the left leg, the right leg, the

waist. Okay. So if you sew up the waist, then what you've got is a kind of long, slightly

bent tube like a straw. So you had three holes, you sewed one up. Now, how many holes

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