Lesson: Jinx Puzzle
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 Teacher
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Here is a puzzle that may surprise you. Follow these steps:

Pick a number (1-10)  __________
Add 11                         __________
Multiply by 6                __________
Subtract 3                    __________
Divide by 3                  __________
Add 5                           __________
Divide by 2                  __________
Subtract the
original number           __________
Your answer is:           __________

Does this puzzle always work? (That is, are you always jinxed with the number 13?)
Try it again with 3 different numbers. (They don't have to be between 1 and 10.)


 First number
 Second number
 Third number
Pick a number


Add 11


Multiply by 6


Subtract 3


Divide by 3


Add 5


Divide by 2


Subtract the original number


Your answer is:



Do you think you will always get 13 no matter what number you try?
Could you find a number that will unjinx the jinx puzzle?

The Jinx Calculator
To help you find out if this puzzle will work for all numbers, we will use a special spreadsheet “calculator." Here's what your Jinx Calculator will look when you open it. Notice that 6 was the chosen number and entered in cell B1.


The spreadsheet then quickly did all the calculations and the answer was once again 13 - the unlucky number. Can you find a number that will make the puzzle not end in 13 (and not jinx you?) Use the Excel version of the Jinx Calculator to help you.

(Hint: Try different kinds of numbers not just whole numbers.  Like these: 2.5, -56, 3000, 999999999, .000005. Fractions can also be tried. For example if you try 1/2, you enter =1/2 into the cell.

Share a few of your interesting examples of numbers that you used here.

Go to the results page and describe the results.

Questions:
What is your conclusion about whether this puzzle always works? Explain.


Is it possible to try all numbers on the spreadsheet? If not, what are some numbers we can't use in a spreadsheet?


Source: Original Version 1.0 developed at CIESE
Center for Innovation in Engineering & Science Education (2007)
Revised 11.13.19 currently under construction