You have a jug of milk from which you have to remove one cup milk aside. but you only have a three-cup measuring container and a five-cup measuring container with you. so how will you remove exactly one cup milk aside?

Assuming the jug has an infinite amount of milk:

Pour into the five cup
Pour the five cups into the three cup, there is now two cups inside of the five cup container and three cups inside of the three cup container
Return the three cups into the jug, so now there is only two cups inside of the five cup container.
Move the two cups into the three cup container. 
Fill the five cup container again, so now there are two cups inside of the three cup container and five cups inside the five cup container.
Pour one cup from the five cup container into the three cup container, now there are three cups inside of the three cup container and four cups inside of the five cup container
Empty out the three cup container, so now there are only four cups inside of the five cup container.
Pour the four cups into the three cups, until you can't anymore, so there are three cups in the three cup container, and one cup in the five cup container.
Pour the three cups back into the container, and you're left with one cup of milk.

I hope this helped, there was probably a simpler way to do this, but whatever.