I think I've worked it out! But I still don't understand why the 43L container is there, could there be a shorter/better solution? Basically I've used a combination of 7s and 11s that add up to 30 : 11 + 11 + 11 + 11 - 7 - 7 = 30 So 1. Pour from 60L to 11L and then to 43L container - you have 11 liters oil in the 43L container now. 2. Pour from 60L to 11L and then to 43L container again - now you have 22 liters oil in the 43L container. 3. Now pour from 43L to 7L to 60L container - you have 15 liters oil in the 43L container. 4. Again, pour from 43L to 7L to 60L container - you have 8 liters of oil in the 43L container. That means you have 22 liters of oil in the 60L container now. Repeat step 1 twice (pour 11 liters twice into the 43L container) and you have 30L oil in the 43L container.