# Subtraction Game & Addition Game – Clobber

Addition Game & Subtraction Game – Clobber is an abstract strategy game invented by mathematicians in 2001. The GoTeachThis version will give your students a real mental workout while they practice addition and subtraction facts.

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# Subtraction Game & Addition Game

## Clobber

Addition Game & Subtraction Game – Clobber

Addition Game & Subtraction Game – Clobber is an abstract strategy game invented by mathematicians in 2001. The GoTeachThis version will give your students a real mental workout while they practice addition and subtraction facts.

Clobber has been played as part of the Computer Olympiad since 2005. This renowned competition is an annual worldwide event that pits accomplished players against each other to determine who is the “world’s best player”.

### Game in a Nutshell:

Subtraction Game – Printer Friendly Version

Players use counters to challenge the position of the other player, adding more counters across the board in an attempt to get the most. Once a player has been challenged for a position, they must correctly solve the associated algorithm.

### Teacher Tip:

Preview the algorithms with your students before you start playing initially in order to make sure they are developing efficient strategies to arrive at the answers to the algorithms. Knowing what to expect will help them to enjoy the game.

### What You Need:

– 2 players
– 1 Clobber Game Board
– 15 white counters
– 15 black counters

Note: Counters don’t have to be black and white – any colored counters will do.

### Before the Game:

Review the rules with students, in particular the way that counters move and what kinds of math problems might be involved. Also review strategy for winning.
All moves must be orthogonal (right angles only along the horizontal and vertical). Review the definition of orthogonal with students.  DIAGONAL MOVES ARE NOT PERMITTED

### GamePlay:

1. The person whose birthday is the next becomes Player One and plays white.
2. Player One picks up one of their counters and taps one of their opponent’s counters which is seated on a vertically or horizontally adjacent square. This move is called a ‘clobber’.
3. Player One removes the ‘clobbered’ counter, answers the algorithm which is revealed & then occupies the space with their counter.
4. Player Two then repeats Steps 2 & 3.
5. Play continues in this fashion until no legal move can be taken.

### Notes on GamePlay:

– Every move MUST be a capture.
– Players cannot slide their pieces onto an empty square.
– Orthogonal moves ONLY (right angles) no diagonals.
– Players cannot capture their own pieces.
During the Game:
• Consider having students stop and record each algorithm if they are ‘struggling’.
• Encourage students to get excited about “clobbering” their opponent! Sound effects are always welcome.
• Offer students strategy hints like:
• Try not to leave your pieces out on their own so they cannot move.
• Try to force your opponent to leave their pieces out on their own so they cannot move.

### Winning:

The winner is the LAST player able to make a legal move i.e. when a player can no longer ‘clobber’ any of their opponent’s pieces they lose.

### Possible Reflection Questions:

– What strategies have you developed to give you a better chance of winning?

– Clobber is such a new game players don’t yet know what is a good way to start. What do you think is the best way to open?

### Possible Extension Activities:

– Invent a differently shaped game board.

– Use different dimensions for the board. How does the gameplay change?

– This is the general rule for making Clobber boards: n x (n+1) where n stands for a number. Ask students what could n x (n+1) mean? Now try making a board with these dimensions.

– Computer Olympiads Clobber is played on 10×10-boards  – Give a 10×10 board a go!

– 5 full-color boards
– 5 low color boards (printer-friendly version)
– 1 PowerPoint Presentation with all full-color boards for easy Number Talks