Most of the time, the maths in our everyday lives works quietly behind the scenes. Until someone forgets to carry a '1' and a bridge collapses, a plane drops out of the sky or a building rocks when its resonant frequency matches a gym class leaping to Snap's 1990 hit I've Got The Power. This book is all about what happens when maths goes wrong in the real world. Exploring and explaining a litany of near-misses and mishaps involving the internet, big data, elections, street signs, lotteries and the Roman empire, Matt Parker shows us the bizarre ways maths trips us all up, and what this reveals about its essential place in our world. Mathematics doesn't have good 'people skills', but we would all be better off, he argues, if we saw it as a practical ally. By making maths our friend, we can use it to our advantage and learn from its pitfalls.