Think of your house number (as long as it's got two digits). Double it. Add 5. Multiply by 50. Add your age. Add the number of days in the year, 365. Subtract 615 and check the result. The first digits are your house number, the last two are your age.

But why?Johnny Ball is well-known for his TV shows in the 1980s such as Think of a Number and Johnny Ball Reveals All. The Ball of Confusion slot first appeared on his daughter Zoe Ball's BBC Radio 2 show in 2008 and has since proved hugely popular, inviting enthusiastic audience participation from across the country. Ball of Confusion features puzzles and problems from the show as well as many more, designed to twist your brain into enjoyable knots of empuzzlement and designed for every level of difficulty - from some solved in a twinkling of an eye to some that will knit your brow for hours.From how to cheat in a coin toss to why it is that some parts of a high speed train travelling at 125mph are actually going backwards, Ball of Confusion will bend your mind in places it's never been bent before. Can you keep up?.