*Adapted from Murderous Maths by Kjartan Poskitt*

**What you need:**

Two people can play, but it’s better with three or more. Each person needs a calculator and a pile of poker chips or counters. Each person will also need scratch paper and a pencil.

**The object of the game:**

First, you have to create your personal defense number by pushing any four buttons on your calculator followed by the = sign. (So you could push 5 ÷ 62 = and your defense number would be 0.0806452.) Other players will try and recreate this same number by pushing four buttons, and if they manage it in time, then you’re dead. Accumulate the most counters and you win!

Note:Any kind of calculator will work great for this game. However, if you have access to a graphing calculator, that will make it easier to notice patterns when you’re trying to solve the defense numbers.

**How to play:**

- To start each player must place two counters into the “bank” (in the center of the table).
- Each player then secretly creates a defense number and must write it clearly on a piece of paper and place it face down in the middle of the table.
- Each player should also make private note of the four buttons that were pushed to create the number.
- When everybody is ready, all the papers in the middle of the table are turned over to reveal the defense numbers! Choose whichever number you think looks easiest and try to crack it first.
- If you think you can create one of the other defense numbers exactly by pushing four buttons and the = on your calculator, you shout, “Fire!” Everybody else stops playing.
- You show which defense number you’ve cracked and demonstrate which buttons you can push to create it.
- If you are right, then that defense number is eliminated and you are awarded one counter from the bank.
- Play continues as everyone tries to crack the remaining defense numbers.
- If you are wrong, then the defense number stays and you must pay another counter to the bank.
- All players keep playing until just one defense number remains. If your number is the last one to survive, then you win all the counters left in the bank. Before claiming the coins, you must demonstrate how you created your defense number. If you can’t, then you don’t get the bank AND you have to pay 5 counters to play in the next round instead of 2.

**Some important details:**

- If your calculator screen is full, then only the first seven digits have to be exact ~ so if the number you were going for is 0.3529411 and you got 0.3529412, then you’ve cracked it!
- It doesn’t matter if the four buttons you use are different from the four buttons the defender used – as long as you get the right answer, then you’ve cracked it!
- People should only use the ten number buttons and the + – x ÷ and decimal point buttons. However, if everybody has a special key like % or ^ , then everyone can agree to use them as one of the four steps. If there is more than one defense number left and nobody can crack them, then after an agreed time limit (say 5 minutes), the bank can be split between the survivors. However, they must each show how they created their number.

*Have fun with math every day!*