Step by step
The question
Question: draw a histogram of 105, 118, 112, 127, 109, 121, 115, 133, 119, 124, 111 and 116, in classes of 10.
How many are less than 120?
1 Make the classes
The smallest number is 105 and the biggest is 133.
In classes of 10: 100 to 109, 110 to 119, 120 to 129 and 130 to 139.
2 Make a frequency table
A frequency table first: one row for each class.
105 is in 100 to 109: a mark there, and we cross out 105.
118 is in 110 to 119.
And so on for every number.
We count the marks: 2, 6, 3 and 1.
3 Draw the bars
Along the bottom: the numbers, from 100 to 140.
Up the side: how many.
100 to 109: 2 numbers.
The bar covers 100 to 110 and goes up to 2.
110 to 119: 6.
120 to 129: 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
100 to 109: 2.
110 to 119: 6.
We add those bars: 2 plus 6 is 8.
5 Check
Let's check: all the bars together are 2 plus 6 plus 3 plus 1, which is 12.
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.