Any real number whose decimal representation terminates or repeats a certain pattern indefinitely is a rational number.
If 0.333330.33333 is intended as just that, i.e. the terminating decimal 0.33333000..., then we can just multiply and divide by a power of 10 to find its fractional representation.
0.33333 = (0.33333xx10^5)/10^5 = 33333/100000
If it is intended as 0.33333... = 0.bar(3), that is, an unending string of 3"'s", then we can divide the repeating portion by 10^k-1, where k is the number of digits the repeating portion. As 3 is what is repeating, and has a single digit, we have
0.33333... = 3/(10^1-1) = 3/9 = 1/3
In either case, we can represent the given number as a ratio of two integers, meaning it is a rational number.
