Compound Units
Use compound units such as speed (distance ÷ time), unit pricing (cost ÷ quantity), and density (mass ÷ volume); solve problems involving compound units
What a learner can do afterwards
- Calculate average speed given distance and time, converting between km/h and m/s if needed
- Compare unit prices of two products sold in different quantities to find the better deal
- Use the density formula to find mass, volume, or density given the other two values
The lesson
Some units come from dividing one measurement by another. Speed is distance ÷ time. Unit price is cost ÷ quantity. Density is mass ÷ volume. These are called compound units.
A cyclist rides 30 km in 2 hours. Speed = distance ÷ time = 30 ÷ 2 = 15 km/h.
A rock has a mass of 150 g and a volume of 50 cm³. Density = mass ÷ volume = 150 ÷ 50 = 3 g/cm³.
Check the units before you divide. If time is in minutes but you want km/h, convert it to hours first. The answer's units come from the division too, like km/h or g/cm³.
Compound units come from dividing one measurement by another: speed, unit price, and density all follow amount ÷ amount, matched to the right units.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.