Until now, it was known that seven times is the magic number for how many times you have to shuffle a deck of cards to get a randomized deck. I didn’t know that some people questioned this assertion and maintained that six is sufficient. Seven is still a better guide, as most people are poor shufflers.

A new paper in Science News tells us that, for games in which some types of randomness are unecessary, four shuffles if sufficient. For instance, in Blackjack, the suits are irrelevant.

Here’s more than you ever wanted to know about shuffling.