← Teacher guide

Rates

Students match rates to distances and times on a double number line, tell rates from ratios, find unit rates and convert between rate units such as km/h and m/s (AC9M8M05, node 1).

Number Foundations · Rates · about 35 minutes · Open the student lesson

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

Students will be able to

Timing

Predict and Run 8 min · Investigate 8 min · Modify 10 min · Practise and Make 9 min

Before class

Do the Run board yourself first. Students need ratios (Number Foundations, Ratios).

The one idea: a rate is "this much per one of that", with two different units; divide the first by the second. The common mistake is dividing the wrong way round (Mia's mistake).

The board's double number line lines up the two quantities; the dashed line marks the unit rate, and the notes give km/h in m/s.

Wider: compare several units for the same speed (km/h, m/s, knots); rates in First Nations land management, such as how fast a cool burn spreads in different conditions (teach with local knowledge where you can).

Running the lesson

  1. Predict: ask what '1 hour's worth' is.
  2. Run: ask what happens to the distance when the time doubles.
  3. Investigate: ask Mia to say her rate in words.
  4. Modify: ask why the cheaper bag is not the better buy.
  5. Make: ask for the speed both ways.

The hard part (on purpose)

Dividing in the right order. Ask students to say the rate in words ('dollars per kilogram') before they divide: the 'per' quantity goes second.

When students get stuck

What you will seeA question to askThe fix
A student divides the wrong way.What is it per? That goes second.Dollars per kilogram = dollars ÷ kilograms.
A student drops the units.60 what, per what?A rate always has two units.
A student multiplies by 3.6 to get m/s.Is a metre per second faster or slower than a kilometre per hour?m/s is the smaller number: divide by 3.6.

Answers to the checks

  1. a car's speed: A car travels 150 km in 2 hours at a steady speed. How far does it go in 1 hour?
    75 km: 150 ÷ 2 = 75. The car's speed is 75 km per hour.
  2. set the rate: Set the rate and the time so that 2 hours matches 150 km. Was your prediction right?

    75 km per hour × 2 h = 150 km.
  3. Rate or ratio: Rate or ratio?
    60 km per hour → Rate; $3.50 per kg → Rate; 2 : 3 cordial to water → Ratio; 80 beats per minute → Rate; 3 boys to 4 girls → Ratio; 7 L per 100 km → Rate
    A rate has two different units; a ratio compares the same kind of thing.
  4. Find the mistake: Mia works out the price of apples per kilogram. Click the line where her working goes wrong.
    line 2
    Line 2: dollars per kilogram is dollars ÷ kilograms: 12 ÷ 3 = $4 per kg. 3 ÷ 12 = 0.25 kg per dollar, a different rate.
  5. Convert a speed: Convert 90 km/h to metres per second.
    25
    90 × 1000 = 90 000 m in 3600 s: 90 000 ÷ 3600 = 25 m/s.
  6. m/s to km/h: Set the rate r (in km/h) so the speed is 25 m/s.

    25 m/s = 25 × 3.6 = 90 km/h.
  7. Price per kilogram: Cheese costs $0.80 per 100 g. What is that in dollars per kilogram?
    8
    1 kg = 1000 g = 10 × 100 g: $0.80 × 10 = $8 per kg.
  8. Best buy: Rice: 600 g for $4.80, or 1 kg for $7.50. Which is the better buy?
    The 1 kg bag: $7.50 per kg, against $8.00 per kg
    4.80 ÷ 0.6 = $8.00 per kg, so 1 kg for $7.50 is cheaper per kilogram.
  9. Heart rate: Your heart beats 18 times in 15 seconds. What is that in beats per minute?
    72
    A minute is 4 lots of 15 seconds: 18 × 4 = 72 beats per minute.
  10. Speed: A train travels 240 km in 3 hours. What is its speed in km per hour?
    80
    240 ÷ 3 = 80 km/h.
  11. Convert: Convert 36 km/h to metres per second.
    10
    36 ÷ 3.6 = 10 m/s.
  12. Price per kg: A 2 kg bag of flour costs $3.40. What is the price in dollars per kilogram?
    1.7
    3.40 ÷ 2 = $1.70 per kg.
  13. Review: ratios: Review: what is the ratio 12 : 18 in simplest form?
    2 : 3
    Divide both by 6: 2 : 3.
  14. a long drive: A drive covers 280 km in 3.5 hours at a steady speed. Set the rate and the time to match.

    280 ÷ 3.5 = 80 km/h.

Solutions

One possible solution for each task. Other correct programs are fine.

convert and compare › m/s to km/h

Open task: any program that does what the step asks.

convert and compare › Price per kilogram

Open task: any program that does what the step asks.

convert and compare › Best buy

Open task: any program that does what the step asks.

convert and compare › Heart rate

Open task: any program that does what the step asks.

a long drive

Open task: any program that does what the step asks.

Stretch and support

Stretch: Express the same speed in km/h, m/s and knots (1 knot = 1.852 km/h). Which unit do ships use, and why?

Support: A card: 'rate = first quantity ÷ second quantity, units: first per second'.

Coach prompt (optional)

For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.

You are a patient maths coach for a Year 8 student in Australia. Help me understand ONE idea only, from the lesson "Rates".

The idea: Rates as comparisons of different units: I can Students recognise that a rate compares two quantities with different units and express rates in standard form (quantity per unit).

What understanding looks like:
- Correctly identifies and writes a rate from a practical context.
- Converts between related rate units.
- Distinguishes a rate (different units) from a ratio (same units).

Mistakes students often make here:
- A student divides the wrong way.
- A student drops the units.
- A student multiplies by 3.6 to get m/s.

How to coach me (rules from the Waypoints Kit coach):
- Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question.
- Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit).
- If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go.
- Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back.
- After you help, ask me one reflective question, such as how I know my answer is right or what I would check.
- Praise my effort and method, not my ability.
- You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so.
- Use simple words.
- Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "Rates".

Exit ticket

A cyclist rides 45 km in 1.5 hours. Find her speed in km/h and m/s.

45 ÷ 1.5 = 30 km/h; 30 ÷ 3.6 ≈ 8.3 m/s.

What each step is for

Where it leads

This starts AC9M8M05.

Where it leads: using rates to solve problems (next lesson), rate models, and gradient as a rate (Linear relations).