1 Why is the unit of pressure caled a derved unit?

Pressure = (force) divided by (area)

But force and area are both derived units themselves.

-- Force = (mass) times (acceleration)

But acceleration is a derived unit itself.

Acceleration = (length) divided by (time squared)

So force = (mass) · (length / time squared)

-- Area = (length squared)

So pressure = (mass · length / time-squared) / (length-squared)

Pressure = (mass) / (length · time-squared)

That sure looks to me like it's derived from a bunch of other stuff.

it has to be b, about 97 percent.

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