You have 2 containers, one can hold 5 cups and the other can hold 3 cups. You have an unlimited supply of water available. How will you Measure out exactly 4 cups?
Fill the 5 cup container full, (5,0)
Fill the 3 cup container full using the 5 cup container, which afterward contains 2 cups, (2,3)
Pour out the 3 cup container and fill it with the 2 cups remaining in the 5 cup container, (0,2)
Fill the 5 cup container, (5,2)
Top off the 3 cup container using the 5 cup container. This takes 1 cup from the 5 into the 3, (4,3)
You now have 4 cups in the 5 cup container.
fill 5 cup......fill 3 cup from 5 cup leaves 2 cups in the larger ....pour out 3 cup and put the 2 cup in it
fill 5 cup again and pour 1 cup in to 3 cup (thus filling the 3 cup container).....now there is 4 cups in 5 cup container.