Line Plots and Scaled Graphs

Grade 3 · Math · Study Guide

Learn how to read and create line plots and scaled bar and picture graphs.

A line plot shows data on a number line by placing an X (or dot) above each value for every time it appears in a data set. For example, if three students are 48 inches tall, there would be three Xs above 48 on the number line. Line plots make it easy to see the most common value and how data is spread out.

A bar graph uses bars of different lengths to show and compare amounts. A scaled bar graph uses a scale where each unit on the axis represents more than 1. For example, if the scale is 'each unit = 5', a bar reaching the 4-unit mark represents 20.

A picture graph (or pictograph) uses pictures or symbols to represent data. A scaled picture graph uses a key to show that each picture represents more than 1 item. For example, if each star = 2 books, then a row of 3 stars represents 6 books.

When reading any graph, always check the scale or key first. When creating a graph, choose a scale that fits all your data without making the graph too large or too small.

Key terms

Line plot: A graph that shows data as Xs or dots on a number line, one mark per data point.
Bar graph: A graph that uses rectangular bars to show and compare amounts of data.
Scale: The numbers on a graph axis that show the value of each unit or interval.
Picture graph (pictograph): A graph that uses pictures or symbols to represent data, with a key showing the value of each symbol.
Key: A label on a graph that explains what each symbol or unit represents.
Data: A collection of facts or numbers gathered to answer a question or solve a problem.

Flashcards

Line plot: Shows data on a number line with X marks. Each X = 1 data point.
Most common value on a line plot: The value with the most Xs — also called the mode.
Scaled bar graph: scale = 2: Each unit on the graph = 2. A bar at height 5 = 5 × 2 = 10.
Picture graph key: Tells you what each picture is worth. Read the key first before interpreting the graph.
Reading a bar graph: Find the top of the bar and read across to the scale on the axis to get the value.
Creating a scaled graph: Choose a scale so bars or data fit the space. Count by 2s, 5s, or 10s if numbers are large.
Why use a scale > 1?: When values are large, using a scale of 2, 5, or 10 per unit keeps the graph a manageable size.
Pictograph: each symbol = 4: 2 symbols = 8 items, 3 symbols = 12 items. Multiply number of symbols by the key value.

Questions

A picture graph has a key: each apple = 3 students. A row shows 4 apples. How many students does that represent?
1. 4
2. 7
3. 12
4. 15
Show answer
Answer: 12
4 apples × 3 students each = 12 students.
On a line plot, each X represents one piece of data.
Show answer
Answer: True
On a line plot, every X stands for one data value. To count how many times a value appears, count the Xs above it.
A scaled bar graph has a scale where each unit = 5. A bar reaches the 6-unit mark. What value does the bar show?
1. 6
2. 11
3. 25
4. 30
Show answer
Answer: 30
6 units × 5 per unit = 30. Always multiply the bar height by the scale value.
On a line plot, the value with the most Xs above it is called the ___.
Show answer
Answer: mode
The mode is the value that appears most often in a data set, shown by the tallest stack of Xs on a line plot.
A class voted on their favorite fruit. The line plot shows: Apple: 5 Xs, Banana: 3 Xs, Orange: 4 Xs. How many students voted in all?
1. 9
2. 10
3. 11
4. 12
Show answer
Answer: 12
5 + 3 + 4 = 12 students voted in total.

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