Four bottles with milk
We have 2 bottles of 10 liter, each filled with milk. Two of your friends having empty bottles of 4 and 5 liter, and want to take 2 liters of milk each. We can use only these 4 bottles (10 l – full, 10 l – full, 4 l – empty and 5 l – empty) to transfer the milk. Wasting or throwing of milk is not permitted. How can this be done? You can not measure milk level by comparing the bottles, it should be exact 2 liters of milk finally in each 4 and 5 liter bottle.