 The name of this game is Number Decoder. This game allows you to practice using mathematical vocabulary to ask questions to help you figure out the hidden two-digit number. You will need a whiteboard, dry erase markers, an eraser, and scratch paper with a pencil. Choose one person to be the number generator. The rest of the players are decoders. Lay the vocabulary cards face up so all of the decoders can read them. The number generator writes down a two-digit number and keeps it hidden. This number is the code number you will try to guess. Now you are ready to play. The player to the left of the number generator goes first. On your turn, choose one vocabulary card. You must ask the number generator a yes or no question using that vocabulary word to help figure out the code number. Is the code number odd? The number generator answers yes or no. In this case, the answer is yes. You may draw a vocabulary card that says freebie. You don't have to use any specific vocabulary word when asking your yes or no question. Is my number less than 30? Yes. Continue rotating turns until 20 questions have been asked or the code number has been determined. Is the number prime? Yes. So the number is odd, prime, and less than 30. What numbers can it be? You may guess the number if you think you know it, but your guess counts as a question if you are wrong. Is the number 19? No. Is the number greater than 19? Yes. That leaves only 23 and 29. We know the number is prime and less than 30. It is also greater than 19. However, the only two odd numbers that are prime and between those two numbers are 23 and 29. It has to be one of those. Is the number 23? Yes. You won the game by identifying the code number. You can continue playing by choosing a new number generator and starting the game over.