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Hello and welcome to More or Less on the BBC World Service,

the programme which really counts. I'm Ruth Alexander.

This week we find out if you can measure the effectiveness of football managers.

But first, here's an email to More or Less at bbc.co.uk that caught our eye.

Dear More or Less, I was watching a music festival on Telly the other day,

and noticed how tightly packed the crowds were.

If all the people in the UK stood shoulder to shoulder,

would they fit into London?

And how much space would all 7 billion people in the world take up?

Looking forward to hearing from you, Jenny, age 12.

Or to answer this, the key bit of information we need to know

is exactly how dense a crowd at a big music festival is.

Well the thing is, with a concert crowd,

it's difficult to get a reliable estimate on density,

not least because people are much more tightly packed at the fronts than the middle and the back.

But here in More or Lessland, we've done a highly scientific experiment

which sort of gets around that density problem.

We measured up the floor space in the studio that isn't taken up by the sound desk

and there were about four square meters.

...