I hated math in school, because if it was not in the book, it was «wrong».
And constant half point due to not showing how it was solved, just correct answere xD
9 multiplication facinate me though, can do loads of «magic» using that xD
You can forexample ask someone to secretly take a forexample 4 digit number - the same number, without telling any numbers. Then ask for the guy to say all but one of the digits and you will know the answere, same with xxx * 9. say all but one number and you will know that last number :D
Here is a Card Trick you can do holding the cards, OR, handing over the cards to the other person and follow your instructions and you will always get the correct card to show up... now, it is like "Memory" ... this is the enticing thing. So, to perform this, you need a standard deck of cards (52) ... so this is what you want them to do, or you are going to tell them what you are going to do.
"I am going to count out 26 cards face up [after shuffling] in a pile and prove I have a great memory."
... note: so you count out 26 cards face up in a pile (on top of each other) without pause with them.
... take that pile and turn it face down and place it under the other stack (basically put the other 26 cards on top)
Flip over the top card... [what ever shows, you ensure it adds up to 10].
... Ace appears... [one + what makes 10?]
... 9 they say, [so place 9 cards FACE DOWN under the ACE]
... now flip over the next card.
... Jack appears... [10 + what makes 10?]
... 0, so you can flip the next card then
... 7 appears ... [7 + what makes 10?]
... 3 they say [so place 3 cards face down under the 7]
... Add up the numbers of the 3 cards faced up.
... Ace = 1, + Jack = 11 and 7 = 18... this is the total.
Okay... count 17 cards from the top of the deck FACE DOWN, leaving the 18th card, and that card will be... (the card you remembered from the first 26 cards counted at the start) ... also note, even if the other person is holding the deck and following your instructions, YOU will still get the right answer.
I am sure you can figure it out from here.