Classic Number Guessing

This trick will impress even your math teacher (but she may already know it).

• Think of a number.
• Double it.
• Add 10 .
• Halve it.
• Take away you original number.
• Is your answer 5?

Try this with a different starting number. Did you get a different result?
Why does this happen?

Write the answer on a piece of paper without letting anybody see it and seal it in an envelope. Have somebody hold the envelope and at the end ask them to open it and reveal the number you wrote at the beginning. Wow, Magic!

You can also try this with a different number than 10 to be added.
What is your result then?

Answer: You can add any number instead of 10 and the final answer will be 1/2 of that number.