# Video: Appropriate Units of Measure

Which quantities could be measured to determine the fuel efficiency of a car? [A] the distance traveled over a good period [B] the quantity of fuel used [C] the fuel price and the distance traveled [D] the distance traveled and the correspomding volume of fuel used. Which of the following is an appropriate unit for measuring fuel efficiency? [A] cubic centimetres per litre [B] cubic centimeters per gallon [C] kilometers per hour [D] miles per hour [E] miles per gallon.

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### Video Transcript

Which quantities could be measured to determine the fuel efficiency of a car?

Fuel efficiency is a kind of ratio. It’s a ratio of the fuel used to the distance travelled with that amount of fuel. Option a) says the distance travelled over a good period.

There’re really two problems here. The first problem is that this is a ratio of distance to time, meaning it’s not a ratio of fuel used to distance travelled. And the second problem is “over a good period” is a nonspecific amount of time. So a) is not the option we’re looking for.

b) The quantity of fuel used. The quantity of fuel used would tell us the quantity of fuel used. But it’s not a ratio. And that means it’s not a measure of efficiency. c) The fuel price and the distance travelled. There’s no direct correlation between the price that you pay for the fuel and the distance you’re able to travel.

And finally option d), the distance travelled and the corresponding volume of fuel used. This is what we’re looking for. We wanna know the ratio of how far you go and the corresponding amount of fuel used to go that far.

With that in mind, let’s consider which of the following is an appropriate unit for measuring fuel efficiency. Remember, this ratio is the distance travelled and the volume of fuel used. a) says cubic centimetres per a litre. Cars do not travel in cubic centimetres. Cubic centimetres is a volume.

And we’ll have the same problem with option b), cubic centimetres per gallon. Again, cars can’t travel by cubic centimetre. Option c) kilometres per hour. Well, cars do travel in kilometres. However, we don’t measure volume of fuel in hours. Miles per hour is option d). Cars can travel in miles. But again hour is not a measure of volume.

Our last option is correct, miles per gallon. Distance travelled, miles, is being compared to the volume of fuel used, gallons.