To expound on Duncan's statement, the equation for a 2-digit number can be
thought of as 10x+y (IOW, ten times the digit in the tens column plus the
digit in the ones column). This means that the equation they are asking you
to use is 10x +y - (x+y) . This can be manipulated to be seen as 10x-x+y-y .
The y cancels itself out and you are left with 9x. As Duncan pointed out,
ALL of the products of 9 have the same symbol (although it is a different
symbol each time). If you doubt it, go ahead and concentrate on any random
number in there and see if it works.
David Lieb
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