How many shuffles does it take to mix a deck of cards?
Trailing the dovetail shuffle to its lair
Mathematicians worked out that you need about seven riffle shuffles to properly mix a deck of cards.
A riffle shuffle is the classic move where you split a deck in two and let the halves flutter together. Two mathematicians, one of them a former magician, asked exactly how many riffles it takes to truly mix a 52-card deck.
The answer is about seven. With fewer, the deck stays surprisingly orderly; after seven, extra shuffles barely help. The title, about trailing a shuffle to its lair, makes it sound like a nature documentary.
Shuffle seven times, then deal with confidence.