Imagine you're a farmer and you've produced a breed of hen that lays particularly strong eggs. You want to test just how strong those eggs are by throwing them off the various floors of a 100-story building. Your task is to find the highest floor you can drop an egg from without breaking it. If you had just one egg, you'd know how you would do this: first throw the egg off the 1st floor, if it doesn't break move up to the second, then the third, and so on. You'd need at most 100 throws to find the answer.
But now suppose you had two eggs. What strategy would you use to find the highest drop an egg can survive? What's the smallest number of egg throws you can get away with?
It's been claimed that this puzzle has been used by Google and/or Microsoft as a job interview question for computer programmers. We came across it on Wild Maths, a website that encourages students to explore maths beyond the classroom and is designed to nurture mathematical creativity. Visit Wild Maths for this and other puzzles and challenges.