Incorrect interpretation of unlabelled mark on y-axis

Student treats the next unlabelled mark from 25 as "half" (0.5) not 2.5.

b)

c)

26

16

Student treats the next unlabelled mark from 25 as "one" (0.5) not 2.5.

b)

c)

28

18

Reads value of unlabelled mark incorrectly

Student follows the line across to the y-axis accurately, but uses the incorrect value of the unlabelled mark.

or

Not following a straight line from the data to the scale on the y-axis

Student doesn't follow the line from the data on the graph to the y-axis accurately,

f) and g)

Not finding the smallest and largest difference correctly

Students identify the application that has the largest or smallest use rather than the largest or smallest "difference".

Next steps:

Incorrect interpretation of unlabelled mark on y-axis

Students who read the unlabelled mark as 0.5% or 1% rather than 2.5%, could be asked to identify and write down all the values on the graph. They could check the y-axis scale to make sure the intervals are equal sized, and discuss how all of the values on the axis must be consistent (in a linear scale).

Not accurately following a straight line across from the data to the scale

Students who may have inaccurately worked out the line as they moved across from the data in the graph to the scale on the y-axis could use a ruler or any straight-line object to guide their eye straight across, and then re-check going back the other way.

Not finding the smallest and largest difference correctly

Students who didn't find the smallest/largest difference, may simply need to explore the meaning of difference, and what a small and large difference mean (and look like). As a simple comparison they could be asked to focus on the first two age groups on the graph and compare them to find the difference.

Are they more or less? How much more? (this is the difference)

Once they have a sense of "difference", get them to look for an application with the largest difference, and then the smallest difference.