According to the National Institute of Environmental Health Sciences, the answer to the riddle "Where do fish keep their money?" is "In a riverbank, of course!" This riddle is an example of a play on words, using two different meanings for "bank" to make the riddle.
This riddle is written for children as it is not particularly difficult to figure out and will amuse younger children the most. A similar riddle would be "What do you get when you cross an automobile with a household pet?" to which the answer is a "carpet," again playing on the word carpet to give it two meanings. These riddles might also be considered jokes by some instead of riddles as they have a humorous aspect.