Question

A 15% tip represents the ratio 15 cents to 100 cents. Why does this make 15% a unit-less factor?

Answer 1

When tipping, if you were to tip 15%, 15 cents would be taken out of every dollar, and that is the amount of the tip. Ex: if you paid 100$ at a restaurant and gave a 15% tip, the tip would be 15$

Answer 2

$\frac{\big{15\ cents}}{\big{100\ cents}} =\frac{\big{15\cdot\ 1\ cent}}{\big{100\cdot\ 1\ cent}} = \frac{\big{15}}{\big{100}} = 15\cdot \frac{\big{1}}{\big{100}} =15\%$