How'd They Do That?

hmmmm

When you do the addition and subtraction, it will always be a multiple of 9, so they just put the same symbal at all the 9 multiples. The add it in a few more places just to be sly, and they use a different symbol each time.

In fact, the 2nd digit does not even matter. Since it is the ones digit, you add in that many ones when you combine the two digits, and you subtract out ones ones (and some more for the 1st digit) when you subtract the new number.

So all that matters is the 1st digit, which is the 10's digit, but gets treated like the one's digit when you just add teh two digit.

So what you are really doing is take any digit, multiple by 10 and subtract the digit.

2 --> 20 - 2 = 18
7 --> 70 - 7 = 63 ... etc

and since 10 times any digit minus 1 times the same digit is the same as 9 times the digit, the answer has to be a multiple of 9.

thats the 1st part of the trick.

putting the same symbol next to eachmultiple of 9 is the 2nd part.