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Maths

Compound measures

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Compound measures

A compound measure is made up of two or more other measurements.

One example of a compound measure is speed. Speed is a compound measure because it is calculated from distance and time.

Look at the triangle below to see the relationship between speed, distance and time.

The formula for working out one measurement can be found by looking at the position of the other two measurements in the triangle. For example, to find distance we multiply speed with time, and to find speed we divide distance with time.

Distance = Speed x Time

Speed = Distance ÷ Time

Time = Distance ÷ Speed

Question

Joe travels 160 miles in 2 hours 30 minutes. What was his average speed?

Solution

  • Speed = Distance ÷ Time

  • 2 hours 30 minutes = 2.5 hours

  • Speed = 160 ÷ 2.5

  • = 64 miles per hour

  • Always remember the units!

Question

A hippo runs at 24 km per hour. How far can it run in 20 minutes?

Solution

The speed we're given is in km and hours, so the time will also need to be in hours. 20 minutes = 20 ÷ 60 or 1/3 of an hour so the hippo ran 24 x 1/3 = 8 km.

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