Arithmetic Methods
Try this...fun for ALL ages: Moebius (Mobius) Strip: This is a video where you see me in person using paper, scissors, and tape, and discover how to make a Moebius strip, as well as some very cool things about it. I've done this with students from kindergarten through college.
These are Alternate Arithmetic Methods to the ones usually taught in schools.
Add from Left to Right (eliminates carrying): http://www.youtube.com/watch?v=eP0mTXLbplo
Subtract from Left to Right: http://youtu.be/NfZ1i5HNcZE
Easy Way to Subtract from 1000: http://youtu.be/1qt10JbQNPg
My Favorite Way to Subtract: http://youtu.be/fzHmE7sSRsY
Cool Way to Subtract by only doing addition: http://youtu.be/bxBPVea0BKU
Multiply using a Grid or Box: http://www.youtube.com/watch?v=d2H1cYTcU4Y
Lattice Multiplication 1 (eliminates carrying): http://www.youtube.com/watch?v=p4Mz0Q-KDFo
Lattice Multiplication 2 more examples (eliminates carrying): http://www.youtube.com/watch?v=NOvWelg2SLM
Lattice Multiplication with Decimals: http://www.youtube.com/watch?v=NX7txf4NWwc
Multiply by 11 the Easy Way: http://www.youtube.com/watch?v=_frb1vznJho
Multiply by 5 the easy way: http://www.youtube.com/watch?v=a0e1gRMavAE
Multiply by 5 the easy way even when you have decimals: http://www.youtube.com/watch?v=2wPAo5YAEfI
Scratch Addition: Quick and easy way to add a column of single digit numbers using the Scratch or Dot Method. http://youtu.be/aobn006_rl0
Multiply by 9 the easy way: multiply single digits by 9, and larger numbers when all the digits are the same, like 88888 x 9: http://www.youtube.com/watch?v=VFHDn4TKHDM
Squaring numbers if all of its digits are ones. Ex: 11 x 11 or 11111 x 11111, etc. Show your friends! http://www.youtube.com/watch?v=xTffv1lpwGg
Square Numbers that end in 5 such as 85 time 85, etc.: http://www.youtube.com/watch?v=Jeh83AoJ0v4