"Oxfam estimates that the richest 85 people in the world own half of all wealth."
This is not what Oxfam's estimates say, it contradicts them. Here is the original quote:
"The bottom half of the world’s population owns the same as the richest 85 people in the world."
This statistic is completely inflammatory and bullshit anyway.
Why?
It uses netto worth so for example academics with student loans and good social security or the bancrupt industrial tycoon are worse off than the indian farmer with his small farm.
That is absolutely not the same. One is referring to half the wealth in the world, one is referring to the wealth owned by the poorest half of the world (which is strictly less than half by definition, and in this case far less than half).
Doesn't make the fact not-disgusting, just slightly less so.
They are not. The bottom 50% of people owns a fraction much smaller than 1/2 of all available wealth.
What Oxfam is saying is: if you rank people by wealth on the x axis then plot their wealth of the y axis, the integral (sum, or area under the curve) of the function on the first half of the graph is equal to the integral on the last 85 points. Try actually drawing it, it might help you understand.
The bottom half of the World's population not only don't have a representative half of the World's wealth, they basically own diddly squat compared to their numbers.