I completed this activity with my students today and it went over well. So I thought I would share it.
Problem: Using clues that are provided to you in the classroom you must determine how old I am. Do not say my age out loud or share your answers with your peers. Simply write your answer in your journal. Once you think you have determined my age, show your answer to me.
Clues: I provided my students with my age in binary code (once on a large post-it in a not so obvious place and then again on a small post-it in an opposite area of the room). This required the use of 6 digits because I am older than 31 =). My students therefore had to stretch what they knew about binary numbers a little to determine my age. (You can use the reward of a prize(s) as an incentive.)