A ratio is simply the way we compare things quantitatively. For instance, if the number of shoes a student has is 6 and the number of books he has is 20. We can use ratios to compare the two quantities.
We say, the ratio of shoes to books is 6:20, the colon sign is used in-between, to separate the quantities.
Rational numbers are numbers that can be expressed in fractional forms. For instance, 0.5 can be expressed as 5/10 or 1/2. Therefore, it is a rational number.