# Calculate expected value when only the marginal probability is known?

I realize this question may not make any sense. I do understand the concept of expected outcome and how it can be used to guide decision making when you know the probabilities, costs, and benefits of certain outcomes.

But what if you don't know the probability of something happening, but rather you know that doing something changes the odds of something happening.

Let's say there is an outcome that is either true or false. There are many unknown variables that effect the outcome. The average probability of this event is also unknown.

If the outcome is true I win $3,000, if not I win nothing. However, I have information on two actions I can take to increase the odds of a true outcome. • Action A: increases the odds of a true outcome by 2%, but costs$200