Albert, Bernard and Cheryl return

Ten years ago I published a maths olympiad question from Singapore on the Guardian website, and it changed my life.

‘Cheryl’s birthday problem’ went viral. Its unexpected success led to the birth of this column in May 2015. And here we are, almost 250 puzzles later.

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17