Line Plots

What is a Line Plot?

A line plot (also known as a dot plot) is a simple way to display data along a number line. It shows the frequency of data points along a number line, using symbols like " $x$ " or dots to represent how many times each value occurs.

Below is a line plot showing the number of cars sold by a dealership on each day of the week:

Parts of a Line Plot

Let's break down what you see on a line plot:

Number Line: The horizontal line that shows the different values (e.g., scores, measurements).
Marks ( $x$ or $dots$ ): These are placed above each value on the number line to show how many times each value occurs.
Labels: The line should be labeled to show what the values represent (e.g., scores, types of shoes).

How to Read a Line Plot

Reading a line plot is like counting the " $x$ "s or dots above each number:

Look at the Number Line: See what each value on the line represents.
Count the Marks: Count how many " $x$ "s or dots are above each value. This tells you how many times that value occurs.
Compare Frequencies: See which values occur most often by checking where the most " $x$ "s or dots are.

Why Use Line Plots?

Line plots are useful because:

They Show Frequency Clearly: You can quickly see which values are most common and how often they occur.
They're Easy to Create and Read: Line plots are simple and straightforward, making them perfect for showing data like test scores, measurements, or counts.

Making a Line Plot

When you make a line plot, here's what you need to do:

Collect Your Data: Determine the values you're plotting (e.g., scores, sizes, counts).
Draw the Number Line: Draw a horizontal line and mark the values you're comparing along the line.
Plot the Marks: For each value, place an " $x$ " or dot above it for each time that value occurs.
Label Everything: Make sure your plot is clearly labeled so it's easy to understand.

infoNote

Worked Example: Student Scores in a Maths Exam

Let's go through an example where we analyse a line plot showing the scores of students in a Maths exam.

The Problem:

The line plot shows the scores (out of $50$ ) for a group of students in a Maths exam. We need to answer the following questions:

Which score was the most common?
How many students scored $34$ ?
How many students scored $45$ or more?

Step 1: Analyse the Line Plot

First, look at the line plot to understand the data:

The horizontal axis (number line) shows the possible scores ( $30$ to $50$ ).
The dots above each score show how many students achieved that score.

Step 2: Answer Each Question

Which score was the most common?

Look for the score with the most dots above it. The score with the highest number of dots is the most common.
For example, if $36$ has the most dots, then $36$ is the most common score.

How many students scored $34$ ?

Count the number of dots above $34$ on the line plot.
For example, if there are $5$ dots above $34$ , then $5$ students scored $34$ .

How many students scored $45$ or more?

Look at the dots above $45, 46, 47, 48, 49$ , and $50$ , and count them all.
For example, if there are $3$ dots above $45$ , $2$ dots above $46$ , and $1$ dot above $48$ , you would add them up: $3 + 2 + 1 = 6$ students scored $45$ or more.

Conclusion

Line plots are a great way to display data when you want to show how often different values occur. They're simple to create and easy to read, making them useful for a variety of data sets, such as test scores, measurements, or counts. By practicing reading and making line plots, you'll become more comfortable with this type of data visualisation.

Line Plots Simplified Revision Notes for Junior Cycle Mathematics