When you measure many things, a line plot shows all the measurements at once. You need to know how to measure with a ruler and how to read graphs.
Why it works
A line plot uses a number line marked like a ruler, in the same unit as the measurements. Each measurement gets one X above its number. So you can see at a glance which lengths are common and how far apart the shortest and longest are.
Worked example: Make the plot
Pencil lengths in inches: 4, 5, 5, 6, 7, 7, 7, 8.
- Draw a number line from 3 to 9, with a mark for every inch.
- Put one X above each length: one at 4, two at 5, one at 6, three at 7 and one at 8.
- Count the Xs: there are 8, one for each pencil.
Answer: the plot above
Worked example: Read the plot
How much longer is the longest pencil than the shortest?
- Longest: 8 inches. Shortest: 4 inches.
- $8 - 4 = 4$.
Answer: 4 inches
Key idea
A line plot puts one X above a number line for each measurement. Count the Xs to answer questions.
Common mistake
Leaving out numbers that have no Xs, so the marks are not evenly spaced. The number line in a line plot must show every number in order, like a ruler. Check: are all the marks the same distance apart?
Grown-up tip: Measure everyone’s hand span or shoe in the family and make a line plot.