Hi, English is not my native language. I manage first time a competition on social media, where: 1. people bring a photo and gather like on it. The top 3 likes will go to final, 2. in the final, they play with a small robot as a vacuum cleaner to clean an area of 1mX1.5m which has 1 pin in every 5cm square of it. Each player will have 5 min to use the robot. I must model so that it will be fair: more chance of making mistake (leaving uncleaned squares) the highest the likes, but how to relate these numbers to squares so it is fair? Currently the top 3 are: a. 84 b. 60 c. 51 I'm sure this is an easy math problem only I can't solve it on the Earth! I don't know even how to google to find similar cases to read about. Could you point me to somewhere to read about this or suggest a fair model please?