Step by step
The question
Question: Data: 4, 6, 7, 9, 29.
Remove 29.
What happens to the mean and the median?
1 Mean before
We add all the numbers, from left to right.
So the total is 55.
There are 5 numbers.
The mean shares the total equally: 55 divided by 5.
So the mean is 11.
2 Median before
The median is the middle number.
For it, the numbers must be in order.
They already are, smallest first.
We cross out the smallest and the biggest, one pair at a time.
And the next pair.
7 is left in the middle.
So the median is 7.
3 Mean after
29 is gone, so the total loses 29.
55 minus 29 is 26.
One number less: now there are 4.
Careful!
We have 4 numbers now, not 5.
So we share by 4.
We share the new total equally: 26 divided by 4.
26 does not share out evenly.
4 times 6 is 24.
2 is left, and 2 divided by 4 is 0.5.
So the new mean is 6.5.
4 Median after
Now the list in order, without 29.
We cross out the smallest and the biggest, one pair at a time.
Two numbers are left in the middle: 6 and 7.
The median is halfway between them: we add them and divide by 2.
6 plus 7 is 13.
13 divided by 2 is 6.5.
5 Compare
The mean went down from 11 to 6.5.
11 minus 6.5 is 4.5.
So it went down 4.5.
The median went down from 7 to 6.5.
7 minus 6.5 is 0.5.
So it went down 0.5.
29 is far from the other numbers.
A far number pulls the mean a lot.
Only the middle numbers matter for the median.
So the far number does not pull it, and it moves just a little.
So the mean goes down 4.5, and the median goes down 0.5.
6 Check
Let's check the new mean: if every number were 6.5, 4 of them would make 6.5 times 4.
That is 26, the new total.
So it is right!
Let's look back.
First: mean before.
Then: median before.
Then: mean after.
Then: median after.
Then: compare.
Last: check.