1. Yourself OR Me.
2. The first coins developed in Iron Age Anatolia and Archaic Greece around 600 BC, so no.
3. Five cats can catch five mice in five minutes. If there were 10 mice running around, how long would it take for those same five cats to catch them? Let's rethink this from the first step. Five cats can catch five mice in five minutes. So, in 10 minutes, they can catch 10 mice. In 20 minutes, they can catch 20 mice.
How many cats are doing the catching? So therefore, the answer is Five. Five cats can catch five mice in five minutes. If the mouse hunt continues another five minutes, you can expect a total of 10 mice to get caught. In other words, the same five cats catch 10 mice in 10 minutes, and 20 mice in 20 minutes. It's simply a matter of how long the five cats work.
4. I assumed Aborted got the right answer?