Step by step
The question
Question: draw a histogram of 8, 15, 22, 11, 19, 26, 13, 17, 24, 16 and 20, in classes of 5.
How many are less than 15?
1 Make the classes
The smallest number is 8 and the biggest is 26.
In classes of 5: 5 to 9, 10 to 14, 15 to 19, 20 to 24 and 25 to 29.
2 Make a frequency table
A frequency table first: one row for each class.
8 is in 5 to 9: a mark there, and we cross out 8.
15 is in 15 to 19.
And so on for every number.
We count the marks: 1, 2, 4, 3 and 1.
3 Draw the bars
Along the bottom: the numbers, from 5 to 30.
Up the side: how many.
5 to 9: 1 number.
The bar covers 5 to 10 and goes up to 1.
10 to 14: 2.
15 to 19: 4.
Careful!
The bars touch.
The numbers go on with no gaps, like a number line.
A bar chart has gaps; a histogram does not.
4 Read the histogram
5 to 9: 1.
10 to 14: 2.
We add those bars: 1 plus 2 is 3.
5 Check
Let's check: all the bars together are 1 plus 2 plus 4 plus 3 plus 1, which is 11.
That is every number in the list.
So it is right!
Let's look back.
First: make the classes.
Then: make a frequency table.
Then: draw the bars.
Then: read the histogram.
Last: check.