One natural question to ask about a probability distribution is, "What is its center? " The expected value is one such measurement of the center. A quick introduction to expected value formulas. How to Use Excel to Calculate Probabilities: Advanced. Expected Value (i.e., Mean) of a Discrete Random Variable. Law of Large To calculate the standard deviation we first must calculate the variance. From the. By calculating expected values, investors can choose the scenario most likely to give them their desired outcome. Getting data from expected value. Computer geld this article help you? There was an error. If you make a chart, the math behind finding an expected value becomes clearer. He began to discuss the problem in a now famous series of letters to Pierre de Fermat. Suppose random variable X can take value x 1 with probability p 1 , value x 2 with probability p 2 , and so on, up to value x k with probability p k. This section explains how to figure out the expected value for a single item like purchasing a single raffle ticket and what to do if you have multiple items. Conceptually, the variance of a discrete random variable is the sum of the difference between each value and the mean times the probility of obtaining that value, as seen in the conceptual formulas below:. The formula will give different estimates using different samples of data, so the estimate it gives is itself a random variable.