Play · Warm-up
Four litres
A 5-litre jug, a 3-litre jug and a tap. Neither jug has markings. End up with exactly 4 litres in a jug.
The puzzle
0 L
5 L jug
0 L
3 L jug
Every step counts. The best answer takes 6.
How to think about it
Work backwards
Work backwards from the goal. 4 litres in the big jug is a full 5 with 1 litre poured out. You can pour out exactly 1 litre if the small jug already holds 2. And 2 is what's left when you pour a full 5 into the 3.