Rational numbers can be expressed as repeating decimals if their denominators (when the fraction is in simplest form) have prime factors other than 2 and 5.
In simpler terms, any fraction that has a denominator that is not composed solely of the factors 2 and 5 will result in a repeating decimal when expressed in decimal form.
If you provide the specific rational numbers you are wondering about, I can help determine which of them can be expressed as repeating decimals.