My guest is Rob Eastaway. Author of many books which make maths more interesting and accessible. He also has a podcast called Puzzling Maths with Andrew Jeffrey which you should check out if by some miracle you’re not getting all your maths vitamins from here. His most recent book is Maths on the back of an Envelope and it’s about the surprising power of mental arithmetic. Along the way, finding out,how to tell the height of a tree using the remains of a savoury snack, estimating crowds, dividing restaurant bills, counting weddings, getting a rough idea of what’s going on using Rob’s favourite word: -ish And generally hopefully, giving us all a bit of confidence to get the answer wrong but close enough. At the very end Ruby takes his advice on board and just start adding stuff up out of the blue. Well not out of the blue, off the milk carton. Follow me on twitter @colmoregan, the podcast @functionroompod. Rob is at https://robeastaway.com/