This game challenges you to determine the correct day of the week for a randomly selected date. Watch this video to learn the Doomsday Algorithm — a set of steps created by my favourite mathematician John Horton Conway to calculate the day of the week for any given date (and it's simple enough you can do it in your head!). Each year has an anchor date (a "doomsday") that falls on the same weekday, and once you know it, you can work out the weekday for most dates quickly.