Issuers tack it on so that the whole card number will satisfy a specific mathematical test—the Luhn algorithm. Here’s how the algorithm works: Write out all but the last digit of the card number.

Murphy, an AI robot equipped with a vision system, central processing unit, and mechanical arm, can scan and sort items on a conveyor belt in seconds.

Algorithmic trading provides a more systematic approach to active trading than one based on intuition or instinct. Learn how hedge funds use computer programs to trade.