The answer to the riddle is the word few. Few is a three-letter word and if you add two more letters, e and r, the word becomes fewer.
The riddle is a phrase, statement or question posed as a poem or puzzle with a hidden meaning meant to be solved. Riddles come in two forms: the enigma and the conundra. To solve a challenging riddle, clever thinking is needed because often the nature of riddles is to utilize double meaning, false concepts and confusing clues. Riddles are considered games, but in ancient times the correct answer or lack of could decide one's fate, life or death.