It is always useful to know how to convert from one system of units into another, and with a little practice it becomes easy. All you need is a basic hand calculator. Here are some exact conversion factors and a few examples. It might behoove the reader to read the section on units first. 1in. = 2.54 cm 1mile = 1.609344 km 1ft = 0.3048 m
Here is how to use these conversion factors. Since these are equalities, one side of the equation can be divided by the other side, and you will still end up with an answer of one, because anything divided by itself is always unity. The conversion factors are 2.54 cm/in., 1.609344 km/mile, and 0.3048 m/ft.
Example 1: Convert 7,956 miles into kilometers:
7,956 miles x 1.609344 km/mile = 12,804 km
This is the diameter of Earth.
Example 2: Convert 299,792 km into miles:
299,792 km/(1.609344 km/mile) = 186,282 miles
This is the approximate distance light travels every second.
Example 3: Now do the first problem using feet and meters:
7,956 miles x (5,280 ft/mile) x (0.3048 m/ft)/(1,000 m/km)
42,007,680 ft x 0.0003048 km/ft
Same answer. How about that!
How do you know when to multiply the conversion factor, and when to divide? Simple. Just look at the units. Always make sure the units you are trying to convert from cancel out, and the units you are trying to end up with are in the numerator. Then you will always get the right answer.
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