Fold one corner of an A4 piece of paper back on itself to make a triangle. Use scissors to cut off the excess paper. Don't forget to grab a grown-up! With the longest side at the bottom, fold the top ...

Mathematician Eugenia Cheng explores the uses of math beyond theclassroom. Read more columns here. I recently had to send a paper letter for the first time in years, so I found myself folding a sheet ...