At 12" depth, 20 tons of gravel will cover 360 sq ft.
It depends how deep you want the gravel to cover, if you want it to be 2 inches deep it's going to cost more than 5 inches. Also it depends how big the gravel is cut, I think that the smaller the gravel is the more it costs.
its really big.. picture it.
The oceans cover an area of 71% of the Earth's surface.
Depends on how big the tiles are.
a gravel road.
The Airpura R600 Air Purifier covers an area of 40 square feet, True HEPA.
W-A-Y too big a question to be covered here. There are tons of books (fiction/non-fiction and textbooks) which cover this subject. Try a search engine.
It could cover an area of 1500 miles by 1500 miles
Yes there are filters for this product. They are not reuseable. The purifier can cover an area of up to 2000 sq. ft.
it rather depends on how thick a layer you put down.
It depends on how big a sheet of plywood you are talking about.
The Big Ben mechanism weighs 5 tons.