Measure six litres
You have an unmarked 4-litre jug and an unmarked 9-litre jug, plus unlimited water. How can you measure exactly 6 litres?
Logic challenge at medium difficulty.
Hint
Create a known remainder by repeatedly filling the smaller jug.
Answer and method
Fill the 9-litre jug. Pour into the 4-litre jug, then empty the 4-litre jug. Pour another 4 litres from the large jug into the small one. The large jug now holds 1 litre. Empty the small jug and move that 1 litre into it. Fill the 9-litre jug again, then top up the small jug with 3 litres. The large jug now contains exactly 6 litres.
Reusable reasoning moveUseful measurements can be created as remainders, not only as direct capacities.