Nines lead to some real fun tricks. One I show my students goes like this:
Think of a fourdigit number. Don't make it something easy like 5555; make it hard.
Now scramble the digits to make a new number.
Subtract the smaller number from the larger number. You'll probably end up with a fourdigit number; if not, tell me the number of digits so I can direct the rest of the trick. (If the person's a prick and gets a onedigit number, you gotta tell them they're a prick and to rescramble; otherwise the adjustments should be obvious).
Take that new fourdigit number and scramble it to get a new number.
Choose one of the digits in that new number and circle it. Don't circle a zero, that's already a circle. (If that line doesn't set off alarm bells in your head, you don't pay much attention to magic tricks). (Don't say that last part).
Take the three uncircled digits, and scramble them to make a new number.
Tell me what that new number is, and I'll tell you what number you circled.
***
As for the 1089 trick, I do it slightly differently: I show kids my new speedreading technique (riffling quickly through the pages of a book) and tell them that I've memorized the book completely. Then we do the addition/subtraction shenanigansif they got a twodigit number after subtraction, it's 99, so I tell them to reverse and add twice instead of once. I tell them to look at the first two digits of their number to choose a page in the book, the third digit to choose the line number on that page, and the final digit to choose the word on that line. They tell me they're on the tenth page, line eight, word nine. I've memorized that sentence, so I make a big show of muttering it to my breath and counting words: "Hmm, Frodo's at the party, he's talking with Samwise, let's see, 'after, the, party, is, finished, would, you, be, so'the word is 'so,' right?"
