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Snap shut on your opponent's caterpillar before they can snap shut on yours.

This is a game of deduction and decimals.

Each team is dealt seven secret cards with numbers chosen from: 3.81, 3.82, 3.83 ... 4 ... 4.19, 4.2, 4.21, 4.22.

(Notice that we use 4 and 4.2 instead of 4.00 and 4.20. This is on purpose so that students get experience ordering numbers with a different number of digits after the decimal point.)

Each team takes time to organize their seven cards to form a caterpillar from smallest (on the left) to largest (on the right). The numbers are kept hidden from the opponents.  Our caterpillar is on the bottom starting with 3.85.

Your opponent's caterpillar is unknown at the top.

Each team gets 5 secret cards in their hand. Ours are shown in the middle of the slide. We can't see the opponent's hand.

On your turn:

1)  Give one of the cards in your hand to your opponent. They must place it in the correct place in their caterpillar.

We know all the numbers to the left of 3.95 are smaller than it, and all the numbers to the right are bigger.

On your turn:

2)  Guess a number that you think is part of the opponent's caterpillar. If you are right, they must flip it over and you get to guess again until you're wrong. Our first guess (4) was right, but our second guess (4.05) was wrong.

On your turn:

3)  Draw a card if there are any left in the deck.

Now it is your opponent's turn, but let's jump forward in the game...

Remember that the cards go from 3.81 to 4.22. Take a moment and try to figure out something about your opponent's caterpillar.

Hint: The two rightmost cards are more than 4.18.

Answer: The two cards on the right must be 4.19 and 4.21 because we can see the other two cards that are more than 4.18.

Okay - it is our turn. Let's give our opponent 3.88 from our hand to place in the correct spot along their caterpillar.

Our opponent places it at the right spot.

Next we will guess a number. Here is where the game gets interesting. We know that the right two numbers are 4.19 and 4.21, but if we guess them now it will give our opponent information about our own card 4.2, so let's wait and guess something we are less sure about... 3.84

We've been lucky. We get to guess again. Let's choose 4.13. Now we know that our opponent will answer no, because it is part of our caterpillar, but this little bit of deception might confuse our opponent.

Lastly we draw a new card.

We win the game if we expose all of our opponent's caterpillar.

Venus Flytrap – dangerous decimals

(MathPickle, 2013)

Here is a pdf to print the cards and rules of the game. Enjoy 😉

Standards for Mathematical Practice

MathPickle puzzle and game designs engage a wide spectrum of student abilities while targeting the following Standards for Mathematical Practice:

MP1 Toughen up!

This is problem solving where our students develop grit and resiliency in the face of nasty, thorny problems. It is the most sought after skill for our students.

MP3 Work together!

This is collaborative problem solving in which students discuss their strategies to solve a problem and identify missteps in a failed solution. MathPickle recommends pairing up students for all its puzzles.

MP6 Be precise!

This is where our students learn to communicate using precise terminology. MathPickle encourages students not only to use the precise terms of others, but to invent and rigorously define their own terms.

MP7 Be observant!

One of the things that the human brain does very well is identify pattern. We sometimes do this too well and identify patterns that don't really exist.


Please use MathPickle in your classrooms. If you have improvements to make, please contact us. We'll give you credit 😉

Gordon Hamilton

(MMath, PhD)


Lora Saarnio