Your example for median salah.The median is the middle number, which always depends on how high is the top number.
If top number for degree holder is $30,000 for people in the 40s, then its median salary will be $15,000....what does that number mean to you? Nothing.
Let me help you with a better example.
If 3 people have income of $100, $500 and $1m. The median would be $500.
You cannot just take 30k and divide by 2. It doesn't work this way.