Mathematical Magic Trick

I’m not sure how I originally ran across this mathematical magic trick, but I think it’s pretty cool.

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. Subtract 5.
5. Determine which letter in the alphabet corresponds to the number you ended up with.
6. Think of a country that starts with that letter.
7. Remember the last letter of the name of that country.
8. Think 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.

Have you been playing along with this mathematical magic trick? If not, you are about to miss out on a lot of fun and unexpected joy. After all, I can’t read your mind and tell you what you are thinking of if you aren’t playing along!

Once you’ve thought of a country, animal, and letter, scroll down. Prepare to have your mind read!

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Are you thinking of a kangaroo in Denmark eating an orange?

According to the University of Waterloo’s math newsletter, 98% of people who complete this activity will end up choosing Denmark, kangaroo, and orange. The newsletter goes into further details about why most people end up with these answers. I found it to be very interesting reading.

I will admit that I was one of the 98% who arrived at that answer when I tried this myself at home.

I used this mathematical magic trick with my students on the second day of school. The results were unexpected.

You see, I assumed that my students would be able to come up with a country that started with the letter D. Nope. One student suggested that maybe the answer was Denver. They told me that they didn’t know the names of countries. Each hour, someone would finally think of Denmark. Then, they would start telling everybody else. And, then they would say their next answer out loud and then their next. So, by the time we got to the end, it wasn’t really “amazing” that I could tell them what their answer was since they had kept saying them out loud.     

Maybe you’ll have better luck than me!

It could also be interesting to have students examine the math behind this. How did we all start with different numbers but end up with the same number?