Concept 5 of 9
The Line Plot: X Marks the Count
Today's big idea
Each X is one item, so the tallest stack names the value that came up most often.
Distance from the leftmost X to the rightmost is the spread of the whole set.
How it works
👀 What's going on?
Twenty children are asked their shoe size, and eight of them say the same number. Writing that number out eight times wastes a line. Stacking eight X's above it does not.
💡 Here's the trick
A line plot is a number line with one X for each item, stacked above the value it belongs to. The tallest stack marks the most common value. The distance from the leftmost X to the rightmost shows the spread, and all the X's added together tell you how many were surveyed.
🪄 How to do it
- 1.Read every X in the picture above as one item sitting at that value.
- 2.Find the tallest stack for the most common value.
- 3.Look at the leftmost and the rightmost X to get the spread.
✍️ Try it
A plot has 3 X's above 2, 5 X's above 3, and 2 X's above 4. How many items were surveyed, and what is the spread?
There are 3 and 5 and 2 X's, so 10 items were surveyed. The X's run from 2 up to 4, so the spread is 4 take away 2, which is 2.
⚠️ Watch out
The tallest stack tells you WHICH value is most common, not how many items there are altogether. Answering 5 for how many were surveyed, when 5 is only the height of one stack, is the trap set here.
🌟 Why this matters
A line plot is what a class survey turns into. Shoe sizes, how many pets each child has, how many books they got through in a month. Anywhere a lot of people give the same answer, stacking beats writing that answer out again and again. Anyone running a survey reaches for one, because the shape of the answer appears as they fill it in.
Exam tip: Count the X's in every stack and write the total in the margin, because most questions need it.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Line plot: 4 X's above 5, 2 X's above 6, 1 X above 7. Most common?”
- 1
Look for the tallest stack
Above 5: 4 X's. Above 6: 2. Above 7: 1.
- 2
Tallest = most common
The X-stack above 5 is the tallest.
- 3
Read the value
That stack sits above the number 5.
- 4
Most common ✓
Most common value = 5
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Each X = 1 item. The TALLEST stack tells you the MOST common value.
Pencils per Student
← number of pencils →
Tap the value with the MOST items (tallest stack).
Quick check
✅ VERIFICATION
On a line plot the X's run from 3 at the left to 9 at the right. What is the spread?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Mode & Range
Mode = most common. Range = biggest minus smallest.