Those with poor color vision may have trouble distinguishing between:
a.
reds and greens
b.
orange and yellows
c.
blues and greens
d.
all colors

i dont feel like thinking ya dig hehe

A. Reds and Greens

Explanation:

people with dueteranomaly and protanomaly are collectively known as red-green color-blind and they generally have difficulty distinguishing between red, greens, browns and oranges. they also commonly confused different types of blue and purple hues.

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