A fraction is mainly used to show the ratio between two quantities.
Having one in the numerator of a unit rate means that for every "one" unit of the numerator there are "n" units of the denominator.
Examples to illustrate this:
\(\frac{boys}{girls} = \frac{1}{3}\)
This means that in a certain place, for every one boy there are 3 girls
\(\frac{days}{pages}\) = \(\frac{1}{5}\)
This means that for every day you read 5 pages
Hope this helps :)
