When I use an assignment like this, I print pages 1 and 2 double sided so that each student has their own copy to work off of. Pages 3-10 are then only printed once and cut in half and scattered randomly through the room or hallway. Students then have the opportunity to work and check their own answer at their leisure.
I have assignments like this due to sometimes students like to sit while others like to stand and move around, this gives them a little more option, plus it is easy to check as when you look at the answer to the riddle, the wrong letters tell you immediately where the mistake is and you can work with the student on that problem.
Page 11 and 12 are a worked out key in case it is needed.