Step by step
The question
Question: draw a box plot of 9, 14, 11, 7, 16, 12, 10, 18, 13 and 8.
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: 7, 8, 9, 10, 11, 12, 13, 14, 16 and 18.
2 Find the median
10 numbers: two in the middle, 11 and 12.
The median goes between them.
It cuts the list in two halves, 5 numbers each.
The median is halfway between them: we add them and divide by 2.
11 plus 12 is 23.
Divided by 2 is 11.5.
3 Find Q1 and Q3
Q1 is the middle of the lower half: 9.
Q3 is the middle of the upper half: 14.
4 Five-number summary
The five-number summary: the smallest 7, Q1 9, the median 11.5, Q3 14, and the biggest 18.
5 Draw the box plot
A number line from 7 to 18.
The box goes from Q1, 9, to Q3, 14.
A line across the box at the median, 11.5.
The whiskers reach out to the smallest, 7, and the biggest, 18.
6 Check
Let's check: the median has 5 numbers below it and 5 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.