We have that 1 inch is 50 miles. When the problem says to use a proportion, it is telling us to make that previous equation into a conversion factor.
There is 1 inch per 50 miles, or 50 miles per 1 inch.
We write a ratio
[tex] \dfrac{50 \ mi}{1 \ in} [/tex].
We use our conversion factor and multiply across, cancelling units.
[tex](4.5 \ in)(\dfrac{50 \ mi}{1 \ in})=225 \ mi[/tex]
