Quick response codes

Make a treasure hunt, provide a link to extension work, and more using QR codes:

http://teachery.net/how-teachers-can-use-qr-codes/

Shared by one of my pupils - a song about finding the mean, mode and median of a set of data.

http://www.youtube.com/watch?v=QH2obAPwfqk

TED-Ed

As well as the brilliant TED talks, you can now access TED-Ed: short animated lessons, with supplementary material, on a variety of topics.

Super-fast addition

Ask the class for two numbers, for example 3 and 5, and use these to generate 10 terms of a Fibonacci-esque sequence:

3, 5, 8, 13, 21, 34, 55, 89, 144, 233

Ask someone to add these up with a calculator while you add them up in your head.

What is the quick way to do this?

Folding polygons from A sized paper

From Motivate:

Be a paper mathemagician!

Multiplication tricks, part one of many

Squaring a two-digit number ending in 5

The last two digits will always be 25.

To get the first digit(s), take the tens digit of your number and multiply it by the next integer.

Example: 45²

To get the first two digits, multiply 4 by 5 (the next consecutive integer) to get 20. Last two digits are 25. So

45² = 2025.

Dubious proofs, part two

Theorem:

A cat has nine tails.

Proof:

No cat has eight tails. A cat has one tail more than no cat.
Therefore, a cat has nine tails.
(from Math Humor)