Math Is Fun Forum

Fill 3-liter bottle and pour int 5-liter bottle.  You have 3 liters of water and 2 liters of air in the 5-liter bottle.  Now, fill the 3-liter bottle again and pour it into 5-liter bottle until full.  That will leave 1 liter of water in the 3-liter bottle.  Empty 5 liter bottle.  Pour the 1 liter from the 3-liter bottle into the 5-liter bottle.  Now there is 1 liter of water in the 5 liter bottle.  Refill the 3-liter bottle and pour those 3 liters into the 5-liter bottle.  Now you have 4 liters of water in the 5-liter bottle.