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The Birthday Puzzle
Student's page

Create the birthday problem spreadsheet for the puzzle below. See if you can figure out what has to be done in order to figure out how this "mind reading" trick works.

  • Ask the participants to write down the number of the month of the year in which they were born.
  • Write the number of the day they were born.
  • Have them do the calculations listed below.
  • Ask a participant what number they got. From that number the Math Magician hears, he or she can determine the person’s birthday. See if you can figure out what he does.
Here is the information the "magician" asks for
    • Month of Birthday
    • The number of the day of birthday
    • Multiply month by 5
    • Add 7
    • Multiply by 4
    • Add 13
    • Multiply by 5
    • Add the day of the month
Build the spreadsheet. Collect some data. From the data see if you can figure out what’s going on.. Add one more row to the spreadsheet called "the secret formula" so that the birthday is revealed. 



Hint: If your birthday is on November 5th the number you should get from the spreadsheet is 1310. How can you find the date of your birthday from that number? (Hint Your birthday is 1105 so what if you subtracted 205 from 1310?

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