Whenever a number is expressed, a unit of some kind is used to specify what the number refers to. These are the little words that come after the number, and they help us decide whether to multiply or divide when we do conversions. Units must always be applied consistently and logically. If a Russian cosmonaut is 2 m tall, and an American astronaut is 6 ft tall, the difference in their heights is not 4 m-ft, even though 6 - 2 = 4. The actual difference must be expressed in a single unit.
[2 m] - [6 ft] [(2m) / (0.3048 m/ft)] - [6 ft] [6.56167979003 ft] - [6 ft] 0.56167979003 ft 6.74 in.
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