If 3 cats can kill 3 rats in 3 minutes, how long will it take 100 cats to kill 100 rats?
It will take 3 minutes for 100 cats to kill 100 rats.
1 cat can kill 1 rat in 3 minutes, so 100 cats can kill 100 rats in 3 minutes.
Why this works
This riddle plays with the concept of rate and scaling. The information that "3 cats can kill 3 rats in 3 minutes" implies that each cat kills one rat in that timeframe. Therefore, if you have 100 cats, each cat is still working at the same rate, allowing them to collectively kill 100 rats in the same 3 minutes. The riddle cleverly leads you to think about the number of cats and rats, but since they scale evenly, the time remains constant!