how to solve a fraction word problem ?

Question

my question i am trying to answer is as fallows ;

A patient is supposed to drink a 300-ml bottle of magnesium citrate prior to his X ray study. He has to be able to drink 180ml. what portion of the bottle remains ? (express your answer as a fraction in lowest terms.)

Answer 1

300-180=120ml of the bottle remains.

The proportion of the bottle remaining is 120/300=60×2/(60×5)=⅖ or 40%.