That's not true.
If [tex]x=0.333\ldots[/tex], then [tex]10x=3.333\ldots[/tex]. Then [tex]10x-x=9x=3[/tex], so that [tex]x=\dfrac39=\dfrac13[/tex].
Or perhaps you meant exactly [tex]0.33333333333333[/tex], which is just [tex]\dfrac{33333333333333}{10^{14}}[/tex].
