A Moment of Science

Chain Letter

A Moment of Science gets a chain letter and we discuss the myth behind the whole concept. Time once again for the Mail Bag, when we read your cards and letters and then just happen to know the answers.

Dear Recipient.

Today is your lucky day! This letter has been sent to you by a friend who wants you to receive spiritual and financial success. Just make five copies of this letter and send them to five people you know . . . . .

I’m not reading anymore! This is clearly a chain letter; and not only are they a nuisance, but they are also bad math.

This letter says to make five copies and send them to five people. Then they make five copies. For illustration, let’s assume the unlikely scenario that every person sends the letter to five completely new people, that is, no one has gotten the letter from someone else. It’s a progression mathematicians call “exponential increase.”

We make five copies. Each person we send to then makes five copies. Now there are twenty-five copies. Then if each person sends a copy there will be one hundred and twenty five. Then six hundred twenty-five. Say . . . the amount it goes up by increases a lot with each round!

That’s called exponential increase. If this only happens 15 times, there will be over six billion copies, which is everyone on the planet. Clearly not everybody who throws away a chain letter dies the next week.

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