Skill: Interpret line graphs

A line graph shows how a quantity changes across an ordered sequence, such as days of the week.

To read one:

1. Look at the horizontal axis to see the order, such as days.
2. Look at the vertical axis to see what is being measured and its units.
3. Check the scale on the vertical axis. The numbers might increase by more than $1$.
4. Find a point and read across to both axes.
5. Compare neighboring points to find increases, decreases, or no change.
6. Subtract to find the difference between two values.

Worked example

A line graph shows the number of books a student read each day:

Day	Books read
Monday	$2$
Tuesday	$4$
Wednesday	$4$
Thursday	$7$
Friday	$5$

The graph has:

• Days on the horizontal axis
• Number of books on the vertical axis
• A scale of $1$ book per interval
• Points connected by line segments

Question 1: How many books were read on Thursday?

Find Thursday on the horizontal axis. Move up to the plotted point, then read across to the vertical axis. The point is at $7$.

Answer: $7$ books were read on Thursday.

Question 2: Between which two days did the number stay the same?

Compare neighboring values:

• Monday to Tuesday: $2$ to $4$, an increase
• Tuesday to Wednesday: $4$ to $4$, no change
• Wednesday to Thursday: $4$ to $7$, an increase
• Thursday to Friday: $7$ to $5$, a decrease

Answer: The number stayed the same from Tuesday to Wednesday.

Question 3: How many more books were read on Thursday than on Monday?

Subtract the Monday value from the Thursday value:

$$7-2=5$$

Answer: $5$ more books were read on Thursday than on Monday.

Remember that the connected lines show the pattern from one recorded point to the next. They do not tell you the exact number for a time that was not recorded.