Start the year with brain gym

Let's start 2012 with a brain teaser:
Don't use paper or a pencil, just your brain, be fast as keep adding the numbers, keep the calculator away from you

• Take the 1000 number,
• Add 40,
• Add another 1000,
• Add 30,
• Add again 1000,
• Add 20,
• Add 1000,
• And add 10.

Whats the total?


5000?


You should try again, the number is 4100!!!




What hapened?
Your brain is confused by the sequence of decimal numbers, and automatically jumps to the  higher decimal (que acontece e que a sequência decimal confunde o nosso cérebro, que salta naturalmente para a mais alta decimal (hundreds rather than tens).

Et voilá!
Another brain mistery!


Enjoy!

Tangram- some cool videos about this math puzzle

Today, on invited restless mind, we have some videos for you about Tangram:

And to finish, my favourite:

Et voilá!
7 dancing "tans" to make nice images, can you do it?

Enjoy!

Yet about Tangram- Paradox

Tangram paradoxes are designs that can be built with all the 7 pieces of the game but aparently are contradictory- click here to see the game rules, like the image above:

Fig1

In this image the man design is paradoxical, both designs used the 7 polygons as the rules, but the right one has feet, what makes us think that it used one more piece. But all the rules were respected! How this is possible?

This paradox was first idealized by Henryn Dudeney, and the solution is in the next figure:

Fig2

After observe the figure above we can conclude that this two images apparently the same, are in fact two different designs with the same area, since the missing feet are compensated by the larger body.. They have the same area because they both use the same polygons (7 tans).
Try to build these figures with your child, and you will see him/her thinking that’s magic.
Now that we understand this dynamic we can see other examples:

Click to expande

Et Voilá!

Fun with geometry

Enjoy!