To solve this problem, set up what is given to us: 4 bags of milk are used per day or 4 bags/ 1 day. We want to find how much time (which is in day) it will take to use 1/2 bag.
So, next is setting up the fractions:
4 bags/ 1 day= (1/2 bag)/ x day
Cross multiply the fractions to get this:
4 bags * x day = 1/2 bag * 1 day
Divide by 4 from both sides to get the answer:
So it will take 1/8 of a day to use 1/2 of a bag of milk.