Acontainer with rounded ends and constructed of heavy gauge metal usually indicates

contents under pressure
contents that are corrosive
contents that are flammable
contents that are liquid

contents under pressure

Explanation:

The gauge of metal describes the thickness of the sheet metal from which the container was made.

Things that have sharp edges would cause stress concentration at the edges. This would be unsafe as the contents might start leaking.

When we round of the edges we are increasing the surface area of the container. This makes the force that the content is exerting on the surface lower making it safer.

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