Step by step
The question
Question: describe the data 3, 3, 4, 4, 4, 8, 9, 9: its center, its spread and its shape.
3, 3, 4, 4, 4, 8, 9, 9
1 Draw a dot plot
A number line from 3 to 9.
One dot for each number.
3 first.
And so on.
2 Find the center
There are 8 numbers.
The middle is between number 4 and number 5.
= 8 numbers: middle = numbers 4 and 5
They are 4 and 4.
Halfway between is 4.
= center: median = 4
3 Find the spread
The spread: biggest minus smallest.
9 minus 3 is 6.
= spread: range = 9 − 3 = 6
4 Describe the shape
The tallest stack, the peak, is at 4.
One peak, at 4.
No dots at 5, 6 and 7: a gap.
Most dots are on the left.
A few spread out to the right: a tail to the right.
= shape: peak at 4, gap at 5, 6 and 7, tail to the right
5 Check
Let's check: we count the dots.
8 dots for 8 numbers.
Every number is crossed out.
So the dot plot is right, and so is the answer!
8 dots, 8 numbers
Let's look back.
First: draw a dot plot.
Then: find the center.
Then: find the spread.
Then: describe the shape.
Last: check.
Answer
= shape: peak at 4, gap at 5, 6 and 7, tail to the right