You toss a coin 50 times and find that the outcome was heads 20 times and tails 30. What is the theoretical probability that the next toss will have an outcome of tails?

The standard answer for this is 50%. However, this is based on the implicit assumption that the coin is fair.

If there are reasonable grounds to doubt that the coin is fair, the theoretical probability must be based on observed statistics. In this scenario, the probability is 60%.