The Guardian – Alex Bellos
“Today’s puzzles were devised by the maths writer Rob Eastaway in a nod to his latest book, Maths on the Back of an Envelope, a joyful primer about the lost art of calculating without a calculator. His book full of insightful tips on how to work things out quickly and sensibly, including a guide to arithmetical rules of thumb and a discussion of the importance of estimation. It’s full of anecdotes too. For example, he writes that back in the 1970s, in the pre-pocket calculator era, cornflakes packets used to display the following mnemonic:” (more)