- Pizza Doubler. The initial problem gives specific dimensions, but the momentum of the problem should be towards a general argument.
- Coin Carpet. If you're going to carpet your floors with any kind of US bill, obviously one-dollar bills get you the same area for the lowest price. But what about coins? If I had a classroom, this problem would run all year. I'd put a bounty on the best coin from around the world. (Something like the slope challenge.) "You found some saucer-sized coin from some obscure island with very favorable exchange rates? Pin the picture to the wall, kid. Nice work."
- Leaky Faucet. I needed this one for PD purposes. As an exercise in rates goes, it's fairly generic, though I wouldn't have guessed anywhere close to the answer.
- Fry's Bank. Timon Piccini posted this video to 101qs.com and I wanted to build a sequel around it.
My students were amazed by the Fry's Bank problem. My favorite part was when a student left out a zero and accidentally calculated the balance after 100 years. $8 after 100 years, but 4 billion dollars after 1,000 years. I had to try it on a different calculator to make sure that his calculator wasn't broken.