The form of is

Let x = 0. = 0.3333... → (eq)1

Since there is only one repeating digit after decimal point, multiply equation 1 by 10.

10x = 3.3333… = 3 + 0.3333… = 3 + x → (eq)2

(eq)2 –(eq)1

10x-x = 3.3333… - 0.3333… = 3

∴ 9x = 3

∴ x = 1/3

Hence, the answer.