How much should Justin and Ron have to bet on red for the bet to be "fair" in their mind?

Different Beliefs and Arbitrage: You sit at a casino's roulette table with two others, Ron and Justin. You hear Ron whisper that he is certain that red only lands around 30% of the time. You hear Justin mumble something similar - that he is certain that red only lands 40% of the time. You know for a fact that the roulette wheel is fair (no O's or 00's), and that the likelihood of red landing is 50%. The roulette payoffs are typical: you double your money when you guess the right color (black, red). 1. Suppose you could offer each a side bet based on their beliefs they bet $X on red, you bet $100 on black, winner takes the pot. How much should Justin and Ron have to bet on red for the bet to be "fair" in their mind? Different Beliefs and Arbitrage: You sit at a casino's roulette table with two others, Ron and Justin. You hear Ron whisper that he is certain that red only lands around 30% of the time. You hear Justin mumble something similar - that he is certain that red only lands 40% of the time. You know for a fact that the roulette wheel is fair (no O's or 00's), and that the likelihood of red landing is 50%. The roulette payoffs are typical: you double your money when you guess the right color (black, red). 1. Suppose you could offer each a side bet based on their beliefs they bet $X on red, you bet $100 on black, winner takes the pot. How much should Justin and Ron have to bet on red for the bet to be "fair" in their mind