You are given 3 containers - pictured in this order below:
- a box with side 2, height 1, and a cone with base radius 1 and height 1 in the middle.
- a box with side 2, height 1, and a half sphere with radius 1 in the middle
- a cylinder with base radius 1 and height 1
The cylinder is full with water. By moving the water between the containers have only 1/3 of the cylinder filled.
Then have the cylinder filled to 2/3. Not very challenging but might be of interest.