Riddles are a great way to start class as a sponge activity. I put these up before class starts and let the students try to solve them. My big problem is preventing them from blurting out the answer! I put a blank on the bottom of our daily worksheet that says "My Brain Torture" answer, but many students are afraid to write down the wrong answer. The good news is once we solve it, they write down the answer. The best news is sometimes the students come up with answers that are better than the original!
These riddles would really be fun for any age, and these are the first in a series of Brain Torture riddles I've used for several years in my classes.
These are Power Point presentations with a standardized background. Press the space bar or use a clicker to advance to the riddle. The second page has the answer. See the sample for details.