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Create and interpret line graphs
Learn step-by-step with practice exercises built right in.
Welcome to line graphs! Line graphs are powerful tools that help us visualize data that changes over time. They make it easy to see trends and patterns at a glance.
A line graph is a type of chart that displays information as a series of data points connected by straight line segments. Line graphs are especially useful for showing how something changes over time.
The title tells you what the graph is about. It should clearly describe the data being shown.
Example: "Temperature in Boston During One Week"
Example: Days of the week (Monday, Tuesday, Wednesday...)
Example: Temperature in degrees Fahrenheit
The scale shows the units and intervals used on each axis. It's important that the intervals are evenly spaced.
This line graph shows temperature throughout the day. At what time was the temperature highest?
Time: 8am(65°), 10am(70°), 12pm(78°), 2pm(82°), 4pm(80°), 6pm(72°)
Look at all the temperatures on the graph: 8am: 65° 10am: 70° 12pm: 78° 2pm: 82° ← Highest point 4pm: 80° 6pm: 72°
The highest temperature is 82°, which occurred at 2pm.
Answer: 2pm (82°F)
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Example: Y-axis might go 0, 10, 20, 30, 40... or 0, 5, 10, 15, 20...
Each point on the graph represents one piece of data. The point shows the value at a specific time or category.
The lines connect the data points in order. They help you see the pattern or trend in the data.
Step 1: Read the title Understand what information the graph shows
Step 2: Look at the axes
Step 3: Find a data point
Step 4: Look for trends
Increasing Trend: When the line goes up from left to right, the values are increasing. Example: A plant's height over several weeks
Decreasing Trend: When the line goes down from left to right, the values are decreasing. Example: Water level in a pool as it drains
Constant (No Change): When the line is horizontal (flat), the values are staying the same. Example: Temperature in a room with thermostat set at 70°
Steep vs. Gradual Changes:
Follow these steps to make your own line graph:
Step 1: Organize your data Make a table with two columns: one for time/category and one for the values
Example: Day | Books Read Mon | 2 Tue | 3 Wed | 2 Thu | 5 Fri | 6
Step 2: Draw and label the axes
Step 3: Choose a scale
Step 4: Mark the intervals Write numbers along each axis at regular intervals
Step 5: Plot the points
Step 6: Connect the points Draw straight lines to connect the points in order from left to right
Step 7: Add a title Write a clear title that describes your graph
When analyzing a line graph, ask these questions:
What is the general trend? Is the data generally going up, down, or staying the same?
When did the biggest change happen? Look for the steepest part of the line
When was there no change? Look for flat sections of the line
What are the highest and lowest points? These are called the maximum and minimum values
Are there any unusual points? Points that don't fit the pattern might indicate something special happened
Line graphs are used to show:
Weather:
Business:
Science:
Personal:
Sports:
Sometimes you'll see more than one line on a graph. This lets you compare two sets of data.
Example: A graph showing temperature for both Boston and Miami over one week
Make sure to include a legend (key) that shows what each line represents!
Not using evenly spaced intervals: The scale must have equal spacing (like 0, 10, 20, 30... not 0, 5, 15, 40)
Forgetting to label axes: Always label what each axis represents and include units
Plotting points incorrectly: Make sure you match the x and y values correctly
Connecting points out of order: Always connect points from left to right in time order
Making the y-axis too short or too tall: Choose a scale that shows all your data clearly
Forgetting the title: Every graph needs a descriptive title
Not starting at zero: Usually the y-axis should start at 0 (though there are exceptions)
When reading a line graph:
When creating a line graph:
Line Graph: Best for showing change over time Bar Graph: Best for comparing different categories Pie Chart: Best for showing parts of a whole Pictograph: Uses pictures to represent data
Choose a line graph when you want to show trends and how data changes continuously!
To master line graphs:
Understanding line graphs helps you make sense of data in the world around you. This skill will be valuable in science, social studies, math, and everyday life!
Using the temperature graph from the previous problem, during which time period did the temperature decrease the most?
Calculate the change for each time period:
8am to 10am: 70° - 65° = +5° (increase) 10am to 12pm: 78° - 70° = +8° (increase) 12pm to 2pm: 82° - 78° = +4° (increase) 2pm to 4pm: 80° - 82° = -2° (decrease) 4pm to 6pm: 72° - 80° = -8° (decrease) ← Largest decrease
The steepest downward line is from 4pm to 6pm.
Answer: 4pm to 6pm (decreased 8°)
A line graph shows plant height over 5 weeks: Week 1(2cm), Week 2(5cm), Week 3(8cm), Week 4(11cm), Week 5(14cm). What is the pattern? Predict the height at Week 6.
Step 1: Find the pattern 5 - 2 = 3cm 8 - 5 = 3cm 11 - 8 = 3cm 14 - 11 = 3cm
The plant grows 3cm each week.
Step 2: Predict Week 6 14 + 3 = 17cm
This would show as a line graph with a constant upward slope (steady increase).
Answer: The plant grows 3cm per week. Week 6 height will be 17cm.
The graph shows money in Sarah's savings account over 6 months. In which month(s) did the amount stay the same?
Jan(75), Mar(100), May(150)
Look for time periods where the line is flat (horizontal).
Jan to Feb: 50 = +100 - 25 (increase) Mar to Apr: 100 = 125 - 25 (increase) May to Jun: 125 = +$25 (increase)
Two students track their reading. In Week 1, both read 2 books. By Week 4, Student A read 8 books total and Student B read 5 books total. If both students' graphs show straight lines, who is reading at a faster rate? How many more books per week?
Student A: Week 1: 2 books Week 4: 8 books Change: 8 - 2 = 6 books in 3 weeks Rate: 6 ÷ 3 = 2 books per week
Student B: Week 1: 2 books Week 4: 5 books Change: 5 - 2 = 3 books in 3 weeks Rate: 3 ÷ 3 = 1 book per week
Compare rates: Student A: 2 books/week Student B: 1 book/week Difference: 2 - 1 = 1 book per week
On a line graph, Student A's line would be steeper.
Answer: Student A is reading faster, by 1 more book per week.
From March to April, the amount stayed at $100.
Answer: March to April (the amount stayed at $100)