Multiplying Decimals at the Casino.

Hello everyone!  I'm really excited as we just started spring break here, so instead of my weekly post I've decided to do a bunch of short success stories from the year.  These are all ideas that I've wanted to blog about, games I've played, or just a-ha moments.  

The first one is a card game I played earlier in the year that helped students reinforce the concept of multiplying decimals.  

Protocol: Decimal Blackjack (or 21 if Blackjack is taboo at your school)

Quick summary: This activity has students practice multiplying decimals.

Materials needed: decks of cards with the 10s, Jacks, Queens, Kings and Aces removed.

Procedure:

1. Put students in partner groups (see my blog on my beliefs of getting into partners here)
2. Give each student a modified deck of cards
3. Ask students who knows how to play 21.  Explain the differences in this game:

• Your goal is to get to .21 or HIGHER without going UNDER.
• You will be multiplying, not adding, your values
• Each card represents a decimal, so 8 is actually .8
• The person closest to .21 without going UNDER wins.

4. Students each draw one card from the deck.  The player with the higher value goes first
5. The student draws a card and multiplies the two values:

This student started with .9 and had to multiply that by .3

6. Play continues until one player goes under .21 (twenty-one hundredths).

I really enjoyed this game.  Rounds went fast (sometimes ending in just one card) which meant lots of repeated practice.   Students quickly made lots of connections to the number line, the algorithm, and reviewed basic facts, but also increased their number sense... Here was one of the big take aways from MANY of my students:

Low numbers "suck" - They learned that when you  multiply by .2 or .3 the value goes down QUICKLY!

Mr. Taylor! I had .9 but then I LOST IN ONE CARD! *SCREAM*

This was by far my favorite unintended consequence of the game.  Building that number sense helps them estimate answers much more accurately and find errors in their thinking in more complex problems.

Students have really enjoyed this game - I've kept it in my game center and they often ask if they can play.  I'm looking for ways to increase the application and metacognition of this activity.  If you have thoughts, please let me know!