William W. answered • 09/03/20
Experienced Tutor and Retired Engineer
I know a few conversion that are floating around in my head so I used them. I know there are 2.54 cm in 1 inch. I know there are 12 inches in 1 foot and 5280 feet in 1 mile. I also know there are 3600 seconds in an hour. So, set up a series of unit factors (1 inch equals 2.54 cm, so since they are the same, and dividing two things that are the same is equal to 1, the number is not "changing" but it is changing form). Like this:
Make sure cm on the top cancels with a cm on the bottom, etc, to yield the units you want (miles/hour). Then just multiply all the numbers in the numerators and divide by all the numbers in the denominators.
145•3600 divided by (2.54•12•5280) = 522000/160934.4 = 3.2436 m/hr (notice I maintain the 5 sig figs)
