What percent of the population really needs to know? How important is it? Would you know how to treat a wound or sprained limb without the use of modern medicine?

I don't know. To me, zips are things to stop your clothes from falling off.

35%

Idk, total guess of like 10%

1%

in the world, I'm gonna say maybe half, thinking about tech savvy kids who can work an iPad from like 5 years old in the West plus China, Japan, it doesn't hurt that many operating systems have native support these days, if you just tap on the file, it will extract the contents automatically - speaking of that, I think a better question is: how many people know how to zip/compress that file, and why they might do it?

35%

World-wide? I have no idea, I don't know in how many countries of what populations computers aren't popular. But in the developed world, I think most people do because I think Windows automatically opens zip files when you double-click them and most people use Windows.

20% . Just a wild guess.