Game in a Nutshell:

Players each receive a target number (one odd, one even) between 1-10. Starting with a 3-digit number above 500, players take turns subtracting numbers and strategically trying to reach their target number.

What You Need:

- 2 players
- 1 calculator per pair
- Recording sheet*
- Pencil

*(NB: A simple recording sheet with columns for ‘Starting Number’, ‘Number Subtracted’ and ‘New Total’ helps students track their thinking)

**Who Goes First? **

- Players decide their targets: Player 1 chooses either odd or even (1-10) and Player 2 takes the opposite type.
- The player with the odd target goes first.

How to Play:

- Players choose a 3-digit whole number above 500 as a starting point
- Player 1 enters this number into the calculator
- Players take turns subtracting a single-digit number from a place value column
- Only the subtraction and numerals keys can be used
- Players must think strategically about place value to reach their target
- The game ends when a player reaches their target number exactly

**An Example Game:**

Player One aims for 4 and Player 2 aims for 7.

The targeting number is 563.

Player One subtracts 400 from 563 on the calculator.

563 – 400 = 163,

Player 2 subtracts 60 to give 103

Explore how the game might continue so players hit their target number.

**How to Win: **

- The first player to reach their exact target number wins.
- If neither player can reach their target, the player closest to their target wins.

**Before the Game:**

- Review place value concepts with 3-digit numbers
- Practice and discuss mental subtraction strategies other than counting backwards
- Explore patterns when subtracting from larger numbers

- Discuss how numbers change from odd to even (and vice versa) when subtracting
- Demonstrate how the calculator’s subtraction function works
- Model thinking aloud: “If I’m aiming for 7 and I have 527 on the display, I could subtract 5 (500) from the hundreds column… this would mean…”

**During the Game:**

- Monitor calculator use – ensure students are only using subtraction
- Watch for understanding of how subtraction affects odd/even numbers
- Note which students are planning ahead vs. random subtraction
- Observe place value understanding in subtraction choices
- Look for students who recognize patterns leading to their target
- Encourage verbal sharing of strategies: “I chose to subtract ___ because…”

After the Game:

- Discuss successful strategies for reaching target numbers
- Create a class list of “What we noticed about subtraction”
- Analyze which starting numbers made the game easier/harder
- Share different paths students took to reach the same target
- Consider how place value knowledge helped strategic thinking

Possible Journal Reflections:

- Today I discovered that when I subtract ___ from an odd number…
- The strategy I used to reach my target was…
- I found it challenging when…
- Next time I play, I will try…
- I noticed a pattern when…

Game Variations:

- Change the range of starting numbers (e.g., 4-digit numbers)
- Allow only certain types of numbers to be subtracted (e.g., multiples of 10)
- Set a maximum number of moves
- Include addition as well as subtraction
- Use decimal numbers for advanced players

Teaching Tips:

- Keep a place value chart visible for reference
- Create a “Strategy Bank” poster with successful approaches
- Use think-alouds to model strategic thinking
- Have students record their moves to analyze later
- Encourage estimation before calculating