Oftentimes when two random variables (X, Y) are observed, the values of the two variables are related. For example, it may be that knowledge about the value of X gives information about the value of Y, even if it does not tell us the value of Y exactly. Conditional probabilities regarding Y given knowledge of the X value can be computed using the joint distribution f(x, y).  Sometimes, however, knowledge about X gives us no information about Y We will discuss these topics concerning conditional probabilities.