The correct answer to this question is C, Probor (a,b) = a+b - ab. This type of question would be found on a math test, specifically for those studying inference and logic. An advanced high school and/or college student would know the correct answer to this question.
This equation is also known as the probability formula. It is the measurement of how probable it is that something will occur. An example of a probability is when it comes to coins. There is a one out of two chance that if the coin is flipped either heads or tails. This equation helps turn a written equation into a mathematical equation.