Is it Magic or Is it Maths?

Stage: 3  

Here are three 'tricks' to amaze your friends.

But the really clever trick is explaining to them why these 'tricks' are maths and not magic. Like all good magicians, you should practise by trying them. Can you explain how they work?

This trick will impress even your maths teacher.

• 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!

https://nrich.maths.org/1051