The word of letters three is six, and once you add two it's three...? Just popped into my head. Correct?
ETA: Oh, duh. I'm stupid. The word of letters three is few, and once you add two it's fewer. :P
(This one is rather long.) You're walking along a path and you come to a fork. One road leads to eternal hell, and the other is glory and happiness. There's a twin by each road. One always tells the truth, and one always lies, but you don't know which is which. You have one question, total, to ask either one of the brothers, to figure out which path to take. What question do you ask?