You have 7 marbles that all appear to be the same, but one is heavier than the others. You have a scale (one with 2 sides where you can compare 2 objects) Your task: Find the heavy marble, but you can only use the scale 2 times!
A neighbor of DH's family asked me this on our most recent trip. When people hear that you are a math person they like to test you (or tell you how much they hate math) I passed the test. Did you?