Step by step
The question
Question: draw a histogram of 15, 22, 18, 31, 26, 19, 24, 28, 17, 33, 21, 25 and 23, in classes of 5.
Which class has the most?
1 Make the classes
The smallest number is 15 and the biggest is 33.
In classes of 5: 15 to 19, 20 to 24, 25 to 29 and 30 to 34.
2 Make a frequency table
A frequency table first: one row for each class.
15 is in 15 to 19: a mark there, and we cross out 15.
22 is in 20 to 24.
And so on for every number.
We count the marks: 4, 4, 3 and 2.
3 Draw the bars
Along the bottom: the numbers, from 15 to 35.
Up the side: how many.
15 to 19: 4 numbers.
The bar covers 15 to 20 and goes up to 4.
20 to 24: 4.
25 to 29: 3.
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
The tallest bar is 15 to 19.
It reaches 4.
So the class with the most is 15-19, with 4 numbers.
5 Check
Let's check: all the bars together are 4 plus 4 plus 3 plus 2, which is 13.
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.