You are in the possession of two bottles, one with a capacity of 7 litres and one with a capacity of 11 litres. Next to you is an infinitely large tub of water.
You need to measure exactly 2 litres in one of the bottles.
You are only allowed to entirely empty or fill the bottles. You can't fill them partially since there is no indication on the bottles saying how much liquid is in them.
How do you measure exactly 2 litres?