When a number is written in decimal form how can you tell if it's a rational number?

We know that a real number is rational if and only if, when expressed as a decimal, it has a finite or recurring expansion.

. . (put a point exactly over 8 and 2).

For example, 5/4 = 1.25, 2/3 = 0.6, 20/7 = 2.857142857 or 20/7 = 2.857142