Are decimals rational

Some are, some aren't.

If the portion after the decimal point:

• terminates (eg 0.125);
• does not terminate, but repeats one or more digits (eg 0.333..., 0.181818...)
• does not terminate, but has one or more digits followed by one or more further digits that repeat (eg 0.16666..., 0.258373737...)

then the decimal is rational.

• otherwise, if the decimal does not terminate and does not repeat any digits (eg Ï€ = 3.1415726..., √2 = 1.41421...)

then the decimal is irrational (not rational).