EXAMPLE 2 What’s That in Feet?

An international student tells his American student friends that he is 180 cm tall. They ask, “How much is that in feet and inches?”

We approach this conversion by using the scaling factor in:

However, because we normally give height in feet and a whole number of inches, the height is

or approximately 5 ft 11 in.

746

Another way to approach the problem is by means of a proportion:

so that

where the cm in the numerator cancels with the cm in the denominator.

A strategy for a calculation requiring two or more conversions is first to plan the calculation: Write out an equation that involves just the units involved in the proportions, leaving out the numbers. Then, after checking that the units cancel correctly, insert the corresponding numbers and do the resulting arithmetic.