1
Checking a dot plot
Discover Mathematics P3: Term 1, Lessons 1–10
GoalCheck a dot plot with a checklist: title, labelled number line, unit, key and neat work.
New words
checklist · a list of things to check one by onelabel · words that name a part of a graphneat · tidy and easy to read
Explanation
Before you hand in a dot plot, check it against a list. Does it have a title that says what it is about? Is the number line labelled, with its unit such as cm? Is there a key that says what one dot means? Are the numbers evenly spaced, and are the dots the same size and in straight stacks? Last, count the dots. The number of dots must be the same as the number of pieces of data. A good dot plot lets a reader answer questions quickly.
| Check | Ask yourself |
|---|---|
| Title | What is the plot about? |
| Number line | Is it labelled with its unit? |
| Key | What does one dot mean? |
| Dots | Are there as many as the data? |
Worked examples
Malak measured 8 leaves. Her plot is titled Leaves in the garden, the number line says length in cm, the key says each dot is 1 leaf, and the dots are neat. Count: 1 + 2 + 3 + 1 + 1 = 8 dots for 8 leaves. It passes the whole checklist.
Seif’s plot has the same dots, but nothing is written under the number line. A reader cannot tell if the numbers are centimetres, millimetres or something else. He must add the label and the unit.
Mina measured 8 ribbons: 6, 7, 7, 8, 8, 8, 9 and 9 cm. Her plot has only 7 dots, because 1 + 2 + 2 + 2 = 7. One dot is missing above 8. She must add a third dot above 8 to get 8 dots.
Class activity
Plot checker. Count the letters in the names of 8 friends or family members and make a dot plot. Swap plots with a partner. Check your partner’s plot with the checklist, and say one thing that is good and one thing to fix.
Practice
1
A dot plot has dots above 3, 4, 4, 5, 5 and 5, but no words under the number line. What is missing?
A label for the number line (with the unit). It also needs a title and a key.
2
Ten children counted the pets they have. Does the plot have the right number of dots?
Yes. 3 + 2 + 4 + 1 + 0 = 10 dots, one for each child.
3
There are 9 pieces of data, but the plot shows only the dots you see. How many dots are missing?
1 dot, because 2 + 3 + 2 + 1 = 8 and 9 − 8 = 1.
4
Write three questions that a reader can answer from a dot plot.
For example: Which number is the most common? How many pieces of data are there? How many are bigger than 5?
5
Habiba says a dot plot is good even if the dots are different sizes and not in straight stacks. Is she right?
No. The dots should be the same size and in straight stacks above the right numbers, so the plot is easy to read.