Step by step
The question
Question: draw a box plot of 1, 3, 5, 7, 9, 11 and 13.
A box plot shows how the numbers spread out.
The box holds the middle half.
1 Put them in order
First we put them in order, smallest first: 1, 3, 5, 7, 9, 11 and 13.
2 Find the median
7 numbers: 3 on each side of the middle one.
The median is 7.
3 Find Q1 and Q3
The median cuts the list in two halves, 3 numbers each.
The median itself is in neither half.
Careful!
The median is not counted in the halves.
Each half has 3 numbers.
Q1 is the middle of the lower half: 3.
Q3 is the middle of the upper half: 11.
4 Five-number summary
The five-number summary: the smallest 1, Q1 3, the median 7, Q3 11, and the biggest 13.
5 Draw the box plot
A number line from 1 to 13.
The box goes from Q1, 3, to Q3, 11.
A line across the box at the median, 7.
The whiskers reach out to the smallest, 1, and the biggest, 13.
6 Check
Let's check: the median has 3 numbers below it and 3 above it.
Each half of the plot holds the same count.
So it is right!
Let's look back.
First: put them in order.
Then: find the median.
Then: find Q1 and Q3.
Then: five-number summary.
Then: draw the box plot.
Last: check.