He uses the major system as a mnemonic method so the error happened when he tried to add “rope”. He accidentally added 47 instead of 49. Great recovery and stage presence. I watch all of his videos cause I’m a huge fan!
This guys been doing his show called "Mathemagics" since the 80s and that's when I first saw him as a kid. He is legendary in the math world for racing against calculators. I wish every maths teacher is an passionate as he is.
Amazing. His computational skills are off the scale. Now I like to know how you develope these impressive skills. Ok, talent is needed. But thats not enough. Loved the show. Hats off😀
The second one is easy to anybody to do!!!! Look at the number he chose: 9216 (a multiple of 9 !!!!!!!!!!!). He got lucky to have one in the board!! Thus, multiplying this number by any number, the result will be a multiple of 9, too!!! When they are saying out loud the digits in the result, he´s adding all of them. Thus, if the sum add to 22........... the digit that wasn´t said is 5 (to add to 27, next multiple of 9). The problem arrives when the "hidden" digit is 0 or 9, ´cause the sum of the others are already a multiple of 9. When I do this trick, I ask first to "cut off the zeros of the result"!!!! Then in the above case, I will know that the hidden digit is 9. Btw, to get a multiple of 9 at the beginning, ask to write any number (which you don´t see... say 257,648), and then to write ANOTHER number with the SAME digits... let´s say he writes 652,874...... and then subtract the smaller from the other ==> 652,874 - 257,648 = 395,226 ====> a multiple of 9........ ALWAYS!!!
I'm actually one of his students at Harvey Mudd College. I got the chance to give him numbers to square on the spot and he did it completely legitimately. I was super impressed.
