Ratios and Rates

Hong Kong

Stage 1 - Stage 3

Lesson

A rate is a ratio between two measurements with different units. A common example of a rate is speed (which is written in kilometres per hour or km/h). You can see that this describes a relationship between two measurements- kilometres and hours.

**Evaluate:** If I drive at $55$55km/hour, how far will I travel in $4$4 hours?

**Think:** $55$55km represents the distance traveled in one hour, so to work out how far I went in $4$4 hours, I would need to multiply this distance by $4$4.

**Do:** $55\times4=220$55×4=220km

These questions don't always use multiplication. Sometimes we need to use division.

What is the speed of a car that travels 56km in 7 hours?

**Evaluate:** If Lee paid $\$11.85$$11.85 for $3$3kg of apples, how much did he pay per kilogram?

**Think: **To find out what $1$1kg costs, we need to divide the weight by $3$3. So we also need to divide the cost by $3$3.

**Do:**$11.85\div3=\$3.95$11.85÷3=$3.95 $/kg$/`k``g`

Convert 300 mL/h to mL/min.

In 2011, the literacy rate in Cuba was 98 people for every 100 in the population. For a town with a population of 83 000, how many literate people would you expect?