Step by step
The question
Question: find the mean of this frequency table.
The values x are 0, 1 and 2.
Their frequencies f are 6, 3 and 1.
x is the value.
f is how many times it comes.
So 0 comes 6 times.
1 Multiply x × f
A new column: x times f.
It is the total of each row.
0 comes 6 times: 0 × 6 = 0.
1 comes 3 times: 1 × 3 = 3.
2 comes once: 2 × 1 = 2.
2 Add the columns
We add the f column: 10 numbers in all.
We add the x × f column: the total of all the numbers is 5.
3 Share equally
The mean shares the total equally: 5 divided by 10.
Careful!
We can't just add 0, 1 and 2 and divide by 3.
There are 10 numbers, not 3.
Each value counts f times.
5 divided by 10 is 0.5.
The books round to one more decimal place than the data.
So the mean is about 0.5.
4 Check
Let's check: if all 10 numbers were 0.5, the total would be 0.5 times 10.
That is 5, the total.
So it is right!
Let's look back.
First: multiply x × f.
Then: add the columns.
Then: share equally.
Last: check.