Our new postcards are too lovely to keep to ourselves! Look behind Door 6 and find out how to get your own set...

It's Cyber Monday and apparently this lunchtime we will all be shopping online. In case you are hunting for presents today, you can find our mathematical suggestions behind Door 5.

The auspicious date of 11/11/11 saw the launch of a brand new YouTube channel dedicated entirely to numbers – it's hiding behind Door 4!

Tennis anyone? Fancy football? Whatever game you are playing (or watching) this weekend, find out the maths behind our two favourite sports behind Door 3.

End of year weariness setting in? Exercise your brain and try some of our favourite puzzles – they're behind Door 2!

What do Caribbean steel drums, the London 2012 Velodrome and the quest for sustainable energy have in common? They all involve the work of engineers. Engineering provides some of the most exciting applications of maths, which impact on all our lives every day. Open Door 1 and discover the mathematics behind engineering.

Most of us take for granted that we can carry our entire music library in our pocket or whip out Google maps on our phones when we get lost. But few of us realise that it's physics and maths we have to thank for these marvellous inventions.

Tomorrow John D. Barrow, cosmologist, best-selling author and director of Plus, will be starting a lecture series on maths and sport at Gresham College in London. The first lecture is entitled How fast can Usain Bolt run? and there'll be five more lectures until the end of March, looking at Olympic sports from rowing to jumping. All lectures are free.