Here’s a fun, very simple classroom game you can play for multiplication.

You may know the game 21, aka blackjack. In classrooms, I like to play with a deck that only includes numbers from 1 to 10.

Twenty-one. Each player gets two cards (face up). They can “hit” to take another card, or “stay” to stick with what they have. Whoever gets as close to 21 without going over wins. (Traditionally this game is played against the dealer in casinos. It’s fine to play it that way as well.)

Here’s how 21 becomes 500:

Five Hundred. Each player gets two cards. As in 21, they can “hit” or “stay.” The difference in 500 is that you multiply the numbers on your cards together. The goal is to get as close to 500 as possible without going over.

So in the image above, the 19 in Twenty-One would be a 240 in 500. Worth sticking in either case.

I only just made this game up last week, and haven’t played too much, so please experiment. Is 500 the best number to have as the bust point? Still, the game makes kids estimate, make a single strategic decision, and multiply one digit numbers and two digit numbers. And it takes almost no time to teach it.

Announcement: Math Salon on August 16!

For Seattleites: we’re happy to announce that we have a Math Salon on the calendar. Supported and hosted at the Greenwood Library, this event is a great opportunity for you and your kids to spend a Saturday afternoon playing with math. If you’re interested in joining us, please rsvp here.

Want to volunteer? Email dan [at] mathforlove.com to join us.