Bagels is a great lesson any time. A student picks a 2 digit number and the other students try and guess the number. After each guess the student at board writes the guess on the board and writes either Bagels, Fermi, or Pico. The class knows that Bagels means neither digits guessed are in the number, Pico means that one of the digits is correct but in the wrong place, and Fermi means that one of the digits is correct and in the correct place. You can't choose double digit numbers. My kids love to play this.