Think of a number.
Multiply it by nine
Add the digits of your answer together
If A=1, B=2, C=3 … what letter is represented by the number you are thinking of now?
Think of a country beginning with that letter
Think of an animal beginning with the second letter of that country
What is the color of that animal?
Is this magic?
You can now investigate the probability of this happening. Having first satisfied themselves that everyone will arrive at the letter D independently of their starting number, how many countries are there starting with D?
How many animals beginning with E? Of all the animals beginning with E how likely is a person to choose elephant? Perhaps a survey might answer this question.
Students could now be asked to make up for themselves a similar trick (but not using Elephants from Denmark). Try out the tricks on some other students and teachers.
Finally, a demonstration of tree diagrams can be used to explain the probabilities of these tricks working.
• Tolstoy: “Some mathematician, I believe, has said that true pleasure lies not in the discovery of truth, but in the search for it.”
• Carl Friedrich Gauss: “I have had my results for a long time: But I do not yet know how I am to arrive at them.”
• Carl Friedrich Gauss: “Mathematics is the queen of science, and arithmetic the queen of mathematics.”
• John von Neumann: “If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.”
• Plato: “I have hardly ever known a mathematician who was capable of reasoning.”
• Archimedes: “Give me a place to stand, and I will move the earth.”
• Rene Descartes: “Perfect numbers like perfect men are very rare.”
• Isaac Newton: “If I have been able to see further, it was only because I stood on the shoulders of giants.”