Water Bottles #1
Obtain exactly 4 gallon of water from a 3 gallon and a 5 gallon container? No, you don't know these two containers' shape. Yes, you only have these two containers and you can't store water anywhere else.
Water Bottles #2
You have three totally unmarked containers: Exactly 8 liters (8LT), 5 liters (5LT), and 3 liters (3LT), respectively. The smaller two containers (the 5LT and 3LT) are empty to start with, and the 8LT container is full with exactly 8LT of water. Your task is to measure out exactly 4LT, using only these three unmarked containers. Without spilling a drop, how do you do it?