Why does plasma challenge what we know about matter? How does it confirm what we already know?

Being made of charged particles, plasmas can do things gases cannot, like conduct electricity. And since moving charges make magnetic fields, plasmas also can have them. In an ordinary gas, all the particles will behave roughly the same way. Auroras, lightning, and welding arcs are also plasmas; plasmas exist in neon and fluorescent tubes, in the crystal structure of metallic solids, and in many other phenomena and objects. The Earth itself is immersed in a tenuous plasma called the solar wind and is surrounded by a dense plasma called the ionosphere.

does anyone know or what?

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form