In probability theory, the expected value of a random variable, intuitively, is the long - run average value of repetitions of the experiment it represents. For example, the expected value in rolling a six - sided die is 3.5, because the average of all the numbers that come up in an extremely large number of rolls is close to 3.5. Less roughly, the law of large numbers states that the arithmetic mean of the values almost surely converges to the expected value as the number of repetitions approaches infinity. The expected value is also known as the expectation, mathematical expectation, EV, average, mean value, mean, or first moment.
what is the expected value of the random variable
the long - run average value of repetitions of the experiment it represents