Two examples coming from Vedic mathematics. Quite useful for mental calculus.
Add or subtract fractions in a graphical way. It's a simple application of the first graphical multiplication trick. In fact, you will combine three multiplications to get a common denominator. The final drawing will have a "M" shape. The upper part shows the numerator, the lower shows the denominator. This trick is NOT meant to be efficient or even useful in everyday life, it's just a graphical, esthetic way to put a calculus. I have also added some info about multiplying by zero since it has been asked before. If you don't understand the video and haven't seen the first multiplication trick, you might want to check it at: www.metacafe.com/watch/296904/easy_mental_multiplication_trick
A nice physics experiment to see! The compression on the sugar crystal, creates a charge separation inside it (a phenomenon called piezoelectricity). This charge separation creates enough current to excite nitrogen in the air. The nitrogen emits light. Wintergreen candies (if you can find them in your country) will make a stronger light. Quartz crystal will do the same and it can even light a LED if connected with. You can also crush the crystal with a pair of pliers. Have you ever tried to smash small sugar cubes in total darkness with a hammer ? It's hard :)
Cool way to fold a letter to the one you love. Perfect for Valentine! Red paper make the hearts look better.
How to transform a multiplication into a simple counting of points through the drawing of a square shape (original analogy was with a stool). It works with any numbers if you keep the right partition. If you use a zero, use a dotted line. When a dotted line cross another dotted line or a plain line, count zero. You can verify with your calculator!It's only meant to be a funny trick to show to kids not to be an efficient way to do multiplication.An application of this trick can be seen at:http://www.metacafe.com/watch/339625/easy_graphical_fractions_addition_subtraction_trick/check our new video: http://www.metacafe.com/watch/410784/eating_fire/