I have a bucket of water that holds 4 gallons of water and another that holds 7 gallons of water. The buckets have no markings. How can I go to the well and bring back exactly 5 gallons of water?

Answer 1

# Start with empty buckets, and carry them to the well. # (Note that the larger is the 7-gallon bucket, and the smaller is the 4-gallon bucket.) # Fill the 4-gallon bucket with water to the top. # Empty all the water from the 4-gallon bucket into the 7-gallon bucket. # (Note that there is room in the 7-gallon bucket for exactly 3 more gallons.) # Fill the 4-gallon bucket again. # Pour from the 4-gallon bucket into the 7-gallon bucket all the water that will fit, spilling none. # (Note that since there was room for only 3 more gallons in the 7-gallon bucket, you now have 1 gallon left in the 4-gallon bucket.) # Dump out all the water from the 7-gallon bucket. (Pour it back into the well or onto some flowers so it's not wasted.) # Pour the 1 gallon of water that remains in the 4-gallon bucket into the empty 7-gallon bucket. # Refill the 4-gallon bucket completely. # Pour all the 4 gallons from the 4-gallon bucket into the 7-gallon bucket. # (Note that since the 7-gallon bucket had 1 gallon already and you added 4 gallons, you now have 5 gallons of water in the 7-gallon bucket!) # Bring back your 7-gallon bucket that's holding exactly 5 gallons of water. (Bring your 4-gallon bucket back too, in case you want to play again!)