You can put a "Hole" to make it lighter...
fill the container with Hydrogen gas(H2)............
A criminal has to carry a sack of stones from one side of the prison to another.
What can he put in the sack that will make it lighter?
There are two plastic jugs filled with water. How could you put all of this water into a barrel, without using the jugs or any dividers and still tell which water camr from which jug?
