Famous Jinx Puzzle
 Student's Page

Collecting Data (3/27/09) session:
Jinx Calculator (Google) (Excel)
Post your candidate to unjinx the jinx puzzle.
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Here are the steps for the Jinx puzzle.

Pick a number     ________
Add 11               ________
multiply by 6      ________
subtract 3         ________
divide by 3         ________
Add 5                ________
Divide by 2        ________
Subtract the
original number   ________

Answer:             ________

Does it always work? Try it with 3 different numbers.


Do you think you will always get 13 no matter what number you try?

The Jinx Calculator
To help you find out if this puzzle will work for all numbers, we will use a special spreadsheet “calculator”. Here is what you do to make one.


  • Open a spreadsheet like Excel to a blank sheet.
  • Type in the text as you see it above.
  • After you finish entering the formulas above, enter a number (like 6) in B1.
  • Look at cell B8. Does it show 13?
You can also download the Excel file with the formulas and text already entered.
For a more Web 2.0 experience access the on-line jinx calculator.

Enter any number in cell B1. Did you get 13 in cell B8? If so that means your number jinxed you. You got 13 - the unlucky number! Can you find a number that will make the puzzle not end in 13? (Try numbers like: 2.5, -56, 3000, 999999999, .000005) Do you think it is possible?

Can you try an irrational number like Pi? What's the problem with that?

Let's try a different way to answer the question. Start with the puzzle again. Only this time we will use bags and marbles.


Step 1: Pick a number.
Instead of picking a specific number, let’s choose to use something that could represent any number. Let’s use a bag.


The bag can contain any number you pick.

Step 2: Add 11



To show 11 we will use 11 small circles or “marbles”. Now we have a bag and 11 “marbles”

Step 3: Multiply by 6


We have 6 bags and 66 marbles.

Step 4: subtract 3


Now we have 6 bags and 63 marbles.

Step 5. Divide by 3


2 bags and 21 marbles.

Step 6. Add 5



2 bags and 26 marbles

Step 7. Divide by 2



1 bag and 13 marbles

Step 8: Subtract the number you picked in step 1.



But that’s the bag. You subtracted the bag! So you are left with 13 marbles or just plain 13.

To see a dynamic version of this proof go to http://www.ciese.org/math/activities/jinx/
For a similar demonstration using X click here.