Skill: Interpret bar graphs

A bar graph uses bars to show amounts for different categories. To read one:

1. Read the title to find out what the graph is about.
2. Look at the category labels along the bottom.
3. Check the vertical axis to see what is being counted and what units are used.
4. Notice the scale intervals on the vertical axis.
5. Find the top of a bar and match it to the scale to determine its value.

Worked example

Suppose a bar graph is titled “Books Read by Students”.

• The horizontal axis lists the students: Ana, Ben, and Carlos.
• The vertical axis is labeled “Number of Books.”
• The scale is marked $(0, 2, 4, 6, 8, 10)$.
• Ana’s bar reaches $6$.
• Ben’s bar reaches $(10)$.
• Carlos’s bar reaches $4$.

Question 1: How many books did Ana read?

Look at Ana’s bar. Its top lines up with $6$.

$$\boxed{6\text{ books}}$$

Even though the scale increases by $2$, Ana’s bar represents $6$, not $3$. The numbers on the axis tell the actual values.

Question 2: How many more books did Ben read than Carlos?

Ben read $(10)$ books, and Carlos read $4$ books. Subtract:

$$10-4=6$$

Ben read $6$ more books than Carlos.

Question 3: How many books did Ana and Carlos read altogether?

Add their values:

$$6+4=10$$

Ana and Carlos read $(10)$ books altogether.

Always use the bar’s height and the axis scale to find each value before comparing or adding.