mathNEWS Issue 89.1: Friday, May 17, 2002

The Mathematics Of ...

Recently, in the mail, I received the following article:


Follow the instructions! NO PEEKING AHEAD! Do the following exercise, guaranteed to raise an eyebrow. There's no trick or surprise. Just follow these instructions, and answer the questions one at a time and as quickly as you can!

  1. Think of a number from 1 to 10
  2. Multiply that number by 9
  3. If the number is a 2-digit number, add the digits together
  4. Now subtract 5
  5. Determine which letter in the alphabet corresponds to the number you ended up with (example: 1=a, 2=b, 3=c,etc.)
  6. Think of a country that starts with that letter
  7. Remember the last letter of the name of that country
  8. Think of the name of an animal that starts with that letter
  9. Remember the last letter in the name of that animal
  10. Think of the name of a fruit that starts with that letter

Are you thinking of a Kangaroo in Denmark eating an Orange?

I told you this was FREAKY!! If not, you're among the 2% of the population whose minds are different enough to think of something else. 98% of people will answer with kangaroos in Denmark when given this exercise.

Freaky, huh?

Being ever so mathematically inclined, I reviewed the steps involved. I recognized that by multiplying any number from 1 to 10 by 9, one receives a multiple of 9: 9, 18, 27, 36, 45, 63, 72, 81, 90. One of the properties of any multiple of nine is that, by adding the digits, one receives a 9 (i.e. (18) 1 + 8 = 9, (27) 2 + 7 = 9, ...). Therefore, all persons taking this 'test' are essentially starting off with the 'random number' 9, and subtracting 5 to get 4. From this 4, each person taking this test then converts it into an appropriate letter — 'D'. Therefore, for this 'test', EVERYONE is starting from the letter 'D'.

We are now expected to find a country starting with the letter 'D'. According to the CIA World Fact Book, we have the following options:

Unfortunately for Dominica, the Dominican Republic, and Djibouti, Denmark is a little more well known (often it is mentioned during an English class while studying Shakespeare's Hamlet, as the play is set in Denmark). This is where one of the choices lie. If one is following instructions and 'answering these questions as quickly as possible,' it is highly probable that you will think of Denmark.

Given the last letter of Denmark, 'k,' we are then required to think of an animal (who doubts the power of the Kangaroo? It's so easy! Outside of Latin phrases, it is unlikely that you will really think of many if any other animals: if you can, then tell me, cause I can't think of any, and haven't found a half decent list on the web yet). [How about the Kiwi, Koala, or Killer Whale? — KreasEd] Thereafter, you must pick a fruit. Given the last letter of the animal's name (Joe-Bob the Kangaroo (o)), 'orange' comes easily to mind.

Hence, the person who originally wrote this established that there are a limited number of countries starting with the letter 'D.' From this, the author then just had to use the properties of multiples of 9 to establish that the person taking the test would only choose a country starting with 'D.' Gotta love math (especially when it doesn't involve derivates).

JB the Kangaroo

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