Step by step
The question
Question: draw a histogram of 23, 37, 41, 28, 35, 44, 31, 26, 39, 33 and 47, in classes of 10.
How many are 30 or more?
1 Make the classes
The smallest number is 23 and the biggest is 47.
In classes of 10: 20 to 29, 30 to 39 and 40 to 49.
2 Make a frequency table
A frequency table first: one row for each class.
23 is in 20 to 29: a mark there, and we cross out 23.
37 is in 30 to 39.
And so on for every number.
We count the marks: 3, 5 and 3.
3 Draw the bars
Along the bottom: the numbers, from 20 to 50.
Up the side: how many.
20 to 29: 3 numbers.
The bar covers 20 to 30 and goes up to 3.
30 to 39: 5.
40 to 49: 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
30 to 39: 5.
40 to 49: 3.
We add those bars: 5 plus 3 is 8.
5 Check
Let's check: all the bars together are 3 plus 5 plus 3, 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.