Amaze your friends by sharing this tricks..

'Mind reading' trick

Choose a single-digit number, multiply it by 9 and if the answer has two digits add them together.

Subtract 5 from what you have, giving you a number. Turn the number into a letter by the rule A = 1, B = 2 and so on. Think of a country beginning with your letter. Take the last letter of your country and think of an animal that begins with that letter. It's odds on that you have a kangaroo in Denmark.

Hailstone numbers

There are many simple questions about numbers that no one has been able to answer.

Start with any number - if it is even divide it by 2, if odd multiply by 3 and add 1 then keep going, writing down the sequence of numbers that you generate. For example, starting with 7 we are led by these rules through the sequence:

7 -> 22 -> 11 -> 34 -> 17 -> 52 -> 26 -> 13 -> 40 -> 20 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1.

It seems no matter what number you start with you eventually hit a 1. These sequences are called the "hailstone numbers" because, like hailstones, they go up and down a number of times before inevitably falling to Earth. However, no one has been able to prove that this has to happen every time.

Threesy does it

You can discover whether a number is a multiple of 3 just by checking whether this is true for the sum of its digits.

For example, 12,894 has 1 + 2 + 8 + 9 + 4 = 24 = 3 x 8, so 12,894 is a multiple of 3.

You don't need to do the long division in order to find this out.

You can do this even for huge numbers that your calculator could never cope with.

For example, try: 111,222,333,444,555,666,777, 888,987. Is it divisible by 3? In fact, if you're clever, you might be able to give the answer before summing the digits.