A median is the middle number in an ordered list of numbers. The “average” is the sum of the numbers divided by how many numbers are on the list. Here is an illustration:
If 10 people each have a net worth of $100, the sum is $1000. That number divided by 10 equals 100 which is the average. Thus the average and the median are the same.
If you change one of those $100 amounts to $1 million, now the sum is $1,000,900. The median is still $100 but the average is 1,000,900÷10, which equals $10,009. That number is not representative of the group at all because it contains such an extreme outlier.
Just think what it would do to the avdrage to have one of the $100 changed to $10 billion. That is like the effect a Jeff Bezos has on statistics.
The devil is in the details - while "average" and "median" seem like they ought to mean about the same thing, in this case it demonstrates that there are a few very wealthy people in a sea of average Joes. The data set was probably something like this:
If the survey has 101 people, and ...
10 people had $100,000 net worth
40 people had $400,000 net worth
1 person had $433,100 net worth - the median: 50 people richer and 50 people poorer than this person
40 people had $500,000 net worth
10 people had $13,568,948 net worth
(10 x 100,000) + (40 x 400,000) + (1 x 433,100 + (40 x 500,000) (10 x $13,568,948), or
1,000,000 + 16,000,000 + 433,100 + 20,000,000 + 135,690,000 = 173,122,585
That's between 101 people, so the average is 173,122,585 / 101 = $1,714,085 average
but the guy with as many people richer than him as are poorer has $433,100 net worth. He's the "median" example. The 10 very rich people skew the average way away from the median. 90% of the people had net worth less than $500,001.
Age range 70-74 Average net worth: $1,714,085 Median net worth: $433,100
That makes no sense at all.
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The difference lies in the number of savers in each saver group. There are many more savers in the low-worth group than the high-worth group. A weighted average would have been most representative of net worth, but readers would have understood that even less.
Weighted average explanation:
https://en.wikipedia.org/wiki/Weighted_arithmetic_mean