At the start of a YouTube video titled “Art of Problem Solving: Least Common Multiple,” Richard Rusczyk invites viewers to play a game. Every twenty-four seconds, we’re supposed to clap; every forty-five seconds, we’re supposed to jump. The challenge is to keep going until we clap and jump at the same time. Rusczyk, who is dark-haired, clean-shaven, and boyish, gestures to a digital timer that appears in a corner of the screen. He starts the clock, stares at it, and fidgets. “Um, how long is this gonna take?” he asks, rolling his eyes like a teen-ager. “I hate waiting.”
When the timer hits twenty-four seconds, Rusczyk claps. When it reaches forty-five, he jumps. Meanwhile, on a digital blackboard, he starts trying to figure out when the clap and the jump will coincide. Over the course of a continuous seven-minute take, Rusczyk jumps and claps at the right times while scribbling equations. First, he tries writing out multiples of twenty-four, but gets bored. Then he tries expressing twenty-four and forty-five as products of their prime-number components: twenty-four is 23 x 31, and forty-five is 32 x 51. “This is gonna work,” he says, clapping. Just as he concludes that it will take three hundred and sixty seconds for the clap and jump to converge, he claps and leaps simultaneously; as it happens, the timer has reached three hundred and sixty. It’s an exuberant, precise performance intended for middle-school kids, or younger ones, who are capable of doing advanced math.
Sourse: newyorker.com
