A conversion is a special type of ratio used to convert from one unit of measurement to another. These ratios are known as conversion factors.


Suppose we wanted to know how many inches are in $3$ feet. Since we know there are $12$ inches in a foot, our conversion factor is $\frac{12\text{ inches}}{1\text{ feet}}$. Thus, there are \[3\;\cancel{\text{feet}}\cdot\frac{12\text{ inches}}{1\;\cancel{\text{feet}}}=\boxed{36\;\text{inches}}\] in $3$ feet.

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