Twenty-One Calculator Activities    blackdouglas.com.au

This easy to learn game can be the basis of a significant problem solving exercise. Apply the strategy of working backwards from 21 by asking:

What number do I have to reach to be certain of being first to 21?

Materials

• One MathMate between two players.

Procedure

The players take turns entering a single digit number and +. The aim is to be the first to reach a predetermined target number such as 21.

• A player who overshoots loses.
• Are there significant numbers prior to reaching the target number?
• Discuss the strategies children are using to arrive at the target.

Variations

1. Start at the target and work back to zero.
2. The person who reaches the target first is the loser.
3. Change the target number at the start of a new round.
4. Limit the numbers which can be added to say 1, 2 and 3.

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