We've already learnt about the concept of a unit rate, which describes how many units of the first type of quantity corresponds to one unit of the second type of quantity.
Now we are going to look at how to compare unit rates, which is a very helpful skill because, for one thing, it can help us work out the best deal on any item we may want to buy.
Basically, when we compare unit rates, we are making a judgement about the characteristics of rates, whether it be which item is the best value (ie. the lowest cost per unit of product) or which line on a graph has greater unit rate.
To find the unit rate:
- from a table or equation, find the constant of proportionality (this will be the unit rate).
- from a graph, find the gradient of the line. The value of the gradient will be your unit rate.
Let's check out some examples below.
Examples
Question 1
Which of the following relationships has the higher unit rate?
$c=10w$c=10w
ALoading Graph...B$c=10w$c=10w
ALoading Graph...B
Question 2
Valentina wants to buy candles. Select the option from the following that offers the best value.
Buy $13$13 candles for $\$18.72$$18.72.
ABuy $4$4 candles for $\$3.52$$3.52.
BBuy $13$13 candles for $\$18.72$$18.72.
ABuy $4$4 candles for $\$3.52$$3.52.
B
Outcomes
NA6-8
Relate rate of change to the gradient of a graph
91028
Investigate relationships between tables, equations and graphs