bearing in mind that a whole is simply same/same or just 1.
3 dozen, there are 3 dozens in 3 dozen, obviously
dozen dozen dozen.
in 2 dozens, there are 2 of course
dozen dozen.
if 3 dozens is three thirds namely 3/3 = 1 = whole, then 2 dozens is just two of those dozens, namely two thirds, 2/3.
so if we use that many ingredients to make a whole three thirds, how much will it be to make only two thirds of it? well, is simply their product, so we'll simply multiply each ingredient amount by 2/3.