Explanation:
a number is rational, if it is a fraction of 2 integers a/b.
that includes integers themselves, as any integer a is also a fraction a/1.
and it includes numbers with endless digits after the decimal point, if there is a repeating pattern of these digits that continues on and on.
7 1/2 is rational (= 15/2)
sqrt(15) is NOT rational.
1.282882882... is rational = 1282/1000 + 882/999000
0 is rational
-8 is rational (= -8/1)
-4/5 is rational
sqrt(81) = 9 is rational