What's a 'firkin'? Is a tardigrade animal, vegetable or mineral? How fast is Usain Bolt ... really? And what's the record for the most lobster rolls eaten in 10 minutes? All these questions and more are answered in Adam Spencer's World of Numbers. This is a book for young and old - for anyone who's ever wondered how things work, who loves puzzles and numbers, or is just plain curious about the amazing world around us. After his bestselling Big Book of Numbers, Australia's funniest and most famous mathematician is back by popular demand.