This is what I learned :
$x = 0.\bar3$ (I)
$10x=3.\bar3$ (II)
(II)-(I) : $9x = 3 => x = 1/3.$ And It's OK.
But now, I think this similar calculation gives me wrong answer:
$x = 0.\bar9$ (I)
$10x=9.\bar9$ (II)
(II)-(I) : $9x = 9 => x = 1$
Why does: $0.\bar9 = 1 $ ?