The answer to the riddle is, "No, they don't have the Vegas idea!" This is a play on words where Vegas stands for "Vaguest," and Vegas is used because of it's reputation with gambling.
Obviously elephants don't have the capability to gamble in reality, but elephants are intelligent creatures capable of many things, such as art.
This riddle is purely for entertainment purposes however, and it has a clever answer with a double meaning as most riddles do. Typically this riddle is used on math worksheets or in a joke book. On math worksheets it is used for simplifying square roots, answering the problems give the answer to the riddle.