Johnny Ball’s book Ball of Confusion is out now.

Buy the book now from Waterstones!

It’s a brilliant collection of puzzles fiendish and perplexing from your favourite TV mathematician, many drawn from his slot of the same name on Zoe Ball’s BBC Radio 2 show. It’s the perfect Christmas present – for yourself or someone else and there’s more about it here…

But here’s your chance to win a copy every Monday-Friday for THE WHOLE OF DECEMBER in association with Waterstones.

Here’s what to do.

1) Login to Twitter and search for the hashtag #johnnyball (or just click here)
2) Wait for today’s question, from @waterstones (so following them would help, too)
3) Once we’ve posted the question, Tweet your answer, ensuring you mention the #johnnyball hashtag

One correct answer randomly selected each day gets a free book – simple!

UK only, sorry!