 There are two solutions to the water jug riddle in the park, at the  elephant fountain. To place exactly 4 gallons of water on the scales  when you only have two jugs which hold 3 and 5 gallons respectively,  you must do either of the following. 1. Fill the 5 gallon jug and  decant the water into the 3 gallon jug. This leaves two gallons in  the big jug. 2. Empty the 3 gallon jug and pour in the two gallons  from the 5 gallon jug, leaving space for one gallon in the small  jug. 3. Refill the 5 gallon jug and pour water from it into the 3  gallon jug until the small jugs full. 4. That leaves exactly four  gallons in the big jug; put it on the scale and the bomb is  disarmed. The second method is: 1. Fill the 3 gallon jug and pour  the water into the 5 gallon jug. 2. Refill the 3 gallon jug, and  pour into the 5 gallon jug until the big jug is full, leaving one  gallon in the small jug. 3. Empty the big jug, and transfer the one  gallon from the small jug to the big jug. 4. Refill the small jug  and pour all three gallons into the 5 gallon jug, resulting in four  gallons in the big jug. Place the big jug on the scale and the bomb  is disarmed.