Practice Set · Part 1
Represent and Describe Data in a Box Plot
Pick up where we left off
Where we left off
Our goal: I can make and read a box plot to summarize a data set, explain what each part stands for, and build one for a situation I have not seen before.
The big idea: The median and quartiles split ordered data into four parts with the same number of values, so the box always holds the middle half.
Model to copy — Example 1 · Even number of values
- Eight students sold 3, 5, 7, 8, 12, 13, 14 and 18 tickets. Find the five numbers for a box plot.
- Find the median of the 8 values: (8 + 12) ÷ 2 = 10
- Split the data into two halves of 4: lower: 3, 5, 7, 8; upper: 12, 13, 14, 18
- Find Q1, the middle of the lower half: (5 + 7) ÷ 2 = 6
- Find Q3, the middle of the upper half: (13 + 14) ÷ 2 = 13.5
- Find the least and greatest values: 3 and 18
- Least 3, Q1 6, median 10, Q3 13.5, greatest 18.
- A box plot shows the scores of 24 students: least 12, Q1 18, median 24, Q3 30, greatest 40. About how many students scored from 18 to 30?
- Find the part that goes from 18 to 30: Q1 to Q3 → the box
- Find half of the 24 students: 24 ÷ 2 = 12
- About 12 students scored from 18 to 30.
Start here
Use the model to solve the first problem. Then try these quick review questions from earlier lessons.
- 1
Same stepsFinish what the group started. Use the model above, step for step.
Try it together — then prove it:- Find the five numbers for a box plot of this data: 2, 5, 5, 8, 11.
- Find the median. (5, the 3rd value.)
- Find Q1 from 2 and 5, and Q3 from 8 and 11. (Q1 is 3.5 and Q3 is 9.5.)
- Find the least and greatest values. (2 and 11)
- Q1 is 3.5, but 3.5 is not in the data. Why is that allowed? (Q1 is the middle of 2 and 5. The middle of two values can fall between them.)
Show your work - 2
Quick reviewThe values 4, 6, 9, 12 and 19 are already in order. What is the median?
- A6
- B9
- C10
- D12
How do you know?
- 3
Quick reviewOrder these values from least to greatest: 6, 13, 4, 9 and 3. What is the median?
- A4
- B6
- C7
- D13
How do you know?
- 4
Quick reviewFind the median of 4, 8, 6, 10.
- A6
- B7
- C8
- D28
How do you know?
Practice Set · Part 2
Represent and Describe Data in a Box Plot
Keep going
Try these on your own
Choose an answer. Then explain how you know.
- 5
Think it throughWhat is Team A's IQR?
- A10
- B16
- C35
- D60
Why is that the answer?
- 6
Think it throughWhat is Team B's IQR?
- A10
- B16
- C45
- D61
How do you know? Give a second reason as well.
- 7
Think it throughIs the fan right that Team B is better because of the 80-point game?
- AYes — 80 is the highest score in the data
- BNo — Team A's maximum is higher
- CYes — the maximum always decides
- DNo — one high game is a single extreme value, not typical performance
Explain your thinking. What would have to change for a different choice to be right?
- 8
Back to the modelThe IQR is Q3 − Q1 = 26 − 10 = 16. What does this tell you about the middle 50% of scorers?
Practice Set · Part 3
Represent and Describe Data in a Box Plot
Words and reasoning
Word bank · Banco de palabras
Use the words
Fill each blank with a word from the bank.
- A graph that shows data with a box and whiskers based on the five-number summary is a ___.
- The middle value of the data, shown as a line inside the box, is the ___.
- A value that divides the data into four equal parts is a ___.
- The distance between the first and third quartiles, showing the middle 50% of data, is the ___.
Explain the thinking
- 9
Find the mistakeRead the mistake. Explain what went wrong, then show the correct step.
The mistake: A common mistake in Display Data: Box Plots is treating a quartile as just one data point instead of the median of a half — for the lower half 4, 8, 10, 14, some students pick 10 (the last value) as Q1 instead of finding the median of that half: Q1 = (8 + 10) ÷ 2 = 9. - 10
Say moreAs you draw the box from Q1 to Q3, what does the length of the box tell you about the players' scores?
- 11
Write your ownWrite your own problem about this situation, then solve it and show the answer. The situation: The table shows 25 sixth graders' times to finish a 5-kilometer road race.
Show your work
Practice Set · Part 4
Represent and Describe Data in a Box Plot
Show what you know
Last check
These two come from Lesson 2.3. If they are shaky, that is the lesson to revisit — not this one.
- 12
Show what you knowExplain your thinking — A box plot has Q1 = 20 and Q3 = 36. What is the IQR and what does it represent?
- AIQR = 16; it is the spread of the middle 50% of the data
- BIQR = 28; it is the median between Q1 and Q3
- CIQR = 36; it is the value of Q3
- DIQR = 56; it is the total of Q1 and Q3
Explain your choice.
- 13
From Lesson 2.3Explain your thinking — Data set: 4, 7, 10, 7, 12. What is the median, and what does it tell you?
- A7 — a typical value in this set is about 7
- B8 — it is the average of all five values
- C10 — it is the middle number as the list is written
- D12 — it is the largest value
How do you know?
- 14
From Lesson 2.3What is the median of the 10 scores?
- A86.6
- B87
- C88
- D92
How do you know?
Check your progress
Choose the box that best describes how you feel about each skill.
| I can… | Not yet | Getting there | Got it |
|---|---|---|---|
| I can make and read a box plot to summarize a data set, explain what each part stands for, and build one for a situation I have not seen before. | |||
| I can explain why it works: The median and quartiles split ordered data into four parts with the same number of values… | |||
| I can justify my answer to a skeptic and connect it to a second strategy or representation. |
One question I want to ask my group next time