Calculating the probability of NOT drawing a traitor card in Dead of Winter
Deal out the four cards in a line.  How likely is it that the one on the far right is the traitor card?  1 in 4 right?  Now have the players pick up everything except the far right card.  What are the chances that they didn't pick up the traitor card?  It's the same question.  So your answer is still 1 in 4.