What's your favourite paradox?

[mgdwszx]

-snip-

Did this recently as an addition to one of the topics I'm studying:
If 0.999... = x
9.999... = 10x
10x - x  would give (9.999... - 0.999...) 9.
9x = 9 so x = 1.

eh?

(...) = recurring decimal
9.999... means the '9' value after the decimal place continues indefinitely (1÷9 = 0.1 recurring, for example)
So if x = 0.999 recurring, multiplying that value by ten will move one nine to the left, giving 9.999...
If you subtract 0.999 recurring from 9.999 recurring you are left with 9, hence my calculation.

edit: the recurring decimal values cancel themselves out