Step by step
The question
Question: draw a histogram of 72, 85, 91, 68, 77, 83, 95, 79, 88, 74, 81, 86, 69 and 92, in classes of 10.
How many are 80 or more?
1 Make the classes
The smallest number is 68 and the biggest is 95.
In classes of 10: 60 to 69, 70 to 79, 80 to 89 and 90 to 99.
2 Make a frequency table
A frequency table first: one row for each class.
72 is in 70 to 79: a mark there, and we cross out 72.
85 is in 80 to 89.
And so on for every number.
We count the marks: 2, 4, 5 and 3.
3 Draw the bars
Along the bottom: the numbers, from 60 to 100.
Up the side: how many.
60 to 69: 2 numbers.
The bar covers 60 to 70 and goes up to 2.
70 to 79: 4.
80 to 89: 5.
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
80 to 89: 5.
90 to 99: 3.
We add those bars: 5 plus 3 is 8.
5 Check
Let's check: all the bars together are 2 plus 4 plus 5 plus 3, which is 14.
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.