Compound Units: Speed, Price, and Density

Mathematics · Ratio & Proportion · ages 11-14

Name ______________________ Date ____________

What is the formula for speed?
- distance ÷ time
- distance × time
- time ÷ distance
To compare unit prices, what do you divide?
- quantity ÷ cost
- cost × quantity
- cost ÷ quantity
What is the formula for density?
- mass × volume
- mass ÷ volume
- volume ÷ mass
54 km/h is the same speed as 15 m/s. True or false?
Circle one: True False
Convert 72 km/h into metres per second.
- 20 m/s
- 72 m/s
- 720 m/s
- 2 m/s
3 kg of flour costs £4.50. What is the price per kg in £?
Answer: ______________
A car travels 120 km in 2 hours. What is its average speed in km/h?
Answer: ______________
A block has mass 500 g and volume 200 cm³. What is its density in g/cm³?
Answer: ______________
Maya says a car going 90 km in 1.5 hours travels at 90 km/h, because 90 is the distance. What is her mistake?
- She divided time by distance
- She used the wrong units
- She didn't divide distance by time
A runner's speed is 36 km/h. What is this in m/s?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

distance ÷ time · Speed tells you how far something goes each unit of time, so you divide distance by time.
cost ÷ quantity · Unit price is the cost of one item or one unit, so you divide the total cost by the quantity.
mass ÷ volume · Density packs mass into a space, so you divide mass by volume.
True · 54 km/h is 54,000 m in 3,600 s, and 54,000 / 3,600 = 15 m/s.
20 m/s · 72,000 m / 3,600 s = 20 m/s.
1.5 · 4.50 / 3 = 1.50 per kg.
60 · 120 / 2 = 60 km/h.
2.5 · 500 / 200 = 2.5 g/cm³.
She didn't divide distance by time · The real speed is 90 ÷ 1.5 = 60 km/h. Maya read off the distance instead of dividing by time.
10 · 36 km/h = 36000 m ÷ 3600 s = 10 m/s.