The purpose of this Warm-up is to elicit the idea that the same data can be displayed in different ways, which will be useful when students create different data displays in a later activity. While students may notice and wonder many things about these images, the comparison of the three representations and interpreting the information in each representation are the important discussion points.
This prompt gives students opportunities to see and make use of structure (MP7). Specifically, they might use the structure of the three representations, particularly the structure of the horizontal number line, to find mathematically important similarities in how the same set of data is represented.
Launch
Arrange students in groups of 2. Display the images for all to see. Ask students to think of at least one thing they notice and at least one thing they wonder. Give students 1 minute of quiet think time, and then 1 minute to discuss with their partner the things they notice and wonder.
Activity
None
Student Task Statement
The dot plot, histogram, and box plot summarize the hours of battery life for 26 cell phones that are constantly streaming video. What do you notice? What do you wonder?
Student Response
Activity Synthesis
Ask students to share the things they noticed and wondered. Record and display their responses without editing or commentary for all to see. If possible, record the relevant reasoning on or near the images. Next, ask students, “Is there anything on this list that you are wondering about now?” Encourage students to observe what is on display and to respectfully ask for clarification, point out contradicting information, or voice any disagreement.
The goal is to help students recall different ways to represent distributions of data. Highlight the similarities between the dot plot and the histogram. Tell students that the tallest bar in the histogram is created from the two data values at 5 and the six data values at 5.5 in the dot plot, and that the final bar is created from the two data values at 6 and the two data values at 6.5 in the dot plot. If time permits, discuss questions such as
“Which representation(s) shows all the data values?” (The dot plot shows all the data values.)
“How do you create a box plot?” (You calculate the values for the five-number summary and then graph them on a number line. The first quartile, the median, and the third quartile are used for the box, and the minimum value and maximum value are used for the whiskers.)
The mathematical purpose of this activity is to represent and analyze data with histograms. Students will create two different histograms from the same data set by organizing data into different intervals.
This activity uses the Stronger and Clearer Each Time math language routine to advance writing, speaking, and listening as students refine mathematical language and ideas.
Launch
Arrange students in groups of 2.
Action and Expression: Internalize Executive Functions. To support organization, provide students with grid or graph paper to organize their two histograms with different interval widths. Supports accessibility for: Language, Organization
2.3
Activity
Optional
10 mins
Tomato Plants: Box Plot
Instructional Routines
None
Materials
None
Activity Narrative
The mathematical purpose of this activity is to represent the distribution of data on the real number line with a box plot and to help students think informally about the median as a measure of center. Students calculate the values for the five-number summary and create a box plot. The median, quartiles, and extreme values split the data set into four intervals, with approximately the same number of data values in each. Students interpret these values in the given context (MP2). Although these intervals are often called “quartiles,” the term “quarters” is used in these materials to avoid confusion with the quartile values Q1 and Q3.
Launch
Keep students in groups of 2. Give students 5 minutes to answer the questions. Ask them to compare their answer with their partner after each question.
Action and Expression: Internalize Executive Functions. To support development of organizational skills in problem solving, chunk this task into more manageable parts. For example, instruct students to refer to their sequential data, divide the data into quarters, and then find the median, Q1, and Q3. Supports accessibility for: Memory, Organization
Lesson Synthesis
In this lesson students viewed data represented by dot plots, histograms, and box plots.
“What are the strengths of each of the representations?” (A dot plot lets you see all of the data and how they are distributed. A histogram summarizes the data using intervals, resulting in fewer columns than in a dot plot. A box plot displays the five-number summary graphically.)
“What are the weaknesses of each of the representations?” (A dot plot has many columns of dots that can make it difficult to determine patterns graphically. Both the histogram and the box plot do not display each individual value in the data set, which means that the mean cannot be calculated directly from either representation.)
“How do you find the ‘typical’ value for a data set?” (You can calculate the mean or median, or estimate the mean or median using a graphical representation.)
Student Lesson Summary
The table shows a list of the number of minutes people could intensely focus on a task before needing a break. Fifty people of different ages are represented.
19
7
1
16
20
2
7
19
9
13
3
9
18
13
20
8
3
14
13
2
8
5
17
7
18
17
8
8
7
6
2
20
7
7
10
7
6
19
3
18
8
19
7
13
20
14
6
3
19
4
In a situation like this, it is helpful to represent the data graphically to better notice any patterns or other interesting features in the data. A dot plot can be used to see the shape and distribution of the data.
There were quite a few people that lost focus at around 3, 7, 13, and 19 minutes, and nobody lost focus at 11, 12, or 15 minutes. Dot plots are useful when the data set is not too large and shows all of the individual values in the data set. In this example, a dot plot can easily show all of the data. If the data set is very large (more than 100 values, for example), or if there are many different values that are not exactly the same, it may be hard to see all of the dots on a dot plot.
A histogram is another representation that shows the shape and distribution of the same data.
Most people lost focus between 5 and 10 minutes or between 15 and 20 minutes, while only 4 of the 50 people got distracted between 20 and 25 minutes. When creating histograms, each interval includes the number at the lower end of the interval but not the number at the upper end.
For example, the tallest bar displays values that are greater than or equal to 5 minutes but less than 10 minutes. In a histogram, values that are in an interval are grouped together. Although the individual values get lost with the grouping, a histogram can still show the shape of the distribution.
Here is a box plot that represents the same data.
Box plots are created using a five-number summary. For a set of data, the five-number summary consists of these five statistics: the minimum value, the first quartile, the median, the third quartile, and the maximum value. These values split the data into four sections, each representing approximately one-fourth of the data. The median of this data is indicated at 8 minutes, and about 25% of the data fall in the short second quarter of the data between 6 and 8 minutes. Similarly, approximately one-fourth of the data are between 8 and 17 minutes. Like the histogram, the box plot does not show individual data values, but other features such as quartiles, range, and median are seen more easily. Dot plots, histograms, and box plots provide three different ways to look at the shape and distribution while highlighting different aspects of the data.
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A histogram can be used to represent the distribution of numerical data.
The data represent the number of days it takes for different tomato plants to produce tomatoes. Use the information to complete the frequency table.
47
52
53
55
57
60
61
62
63
65
65
65
65
68
70
72
72
75
75
75
76
77
78
80
81
82
85
88
89
90
days to produce fruit
frequency
40–50
50–60
60–70
70–80
80–90
90–100
Use the set of axes and the information in your table to create a histogram.
The histogram you created has intervals of width 10 (like 40–50 and 50–60). Use the set of axes and data to create another histogram with an interval of width 5. How does this histogram differ from the other one?
Blank coordinate plane, no grid. Horizontal axis from 30 to 100, by 5's, labeled "days to produce fruit." Vertical axis from 1 to 10 by 1's, labeled "number of tomato plants"