ACT
A simple way to read a graph
Check labels, units, and patterns before you choose an answer.
Read the labels first
Find the title and read both axes. Ask what each axis measures and what units it uses. If a graph shows several lines, read the key before deciding which line belongs to the question.
Find a value
Imagine a graph where the horizontal axis shows hours and the vertical axis shows distance in miles. To find the distance at two hours, start at two on the horizontal axis, move to the relevant line, then read across to the vertical axis. Check the scale before recording the value.
Compare changes
A line that rises shows an increase as you move left to right. A steeper section shows a larger change over the same horizontal distance. Do not compare steepness across different graphs without checking their scales.
Watch for common traps
A graph can start above zero, use uneven intervals, or show more than one series. A high point is not necessarily the largest increase. When a question asks how much a value changed, subtract the earlier value from the later one.
Try it yourself
Suppose a table shows 4, 7, and 9 plants at the end of weeks one, two, and three. The increase from week one to week two is 3 plants; from week two to week three it is 2. The total rises, but the increase gets smaller. This is an illustrative example.
Practice with a small data set
The table below is an invented example. A student records the height of a seedling each week.
| Week | Height (cm) |
|---|---|
| 1 | 3 |
| 2 | 5 |
| 3 | 8 |
| 4 | 9 |
Which interval has the largest increase?
Subtract each pair of neighboring values: 5 − 3 = 2 cm, 8 − 5 = 3 cm, and 9 − 8 = 1 cm. The largest increase is between weeks 2 and 3. Week 4 has the greatest height, but it does not have the greatest increase.
How much did it grow from week 1 to week 4?
Subtract the initial measurement from the final measurement: 9 − 3 = 6 cm. The final height is 9 cm; the amount of growth over the period is 6 cm. The wording of the question tells you which quantity to report.
Check the units
If a different table reports height in millimeters, convert before comparing. One centimeter is ten millimeters, so 3 cm is 30 mm. Record the units alongside your answer so the comparison stays clear.