Expected Value Calculator

This tool works out the expected value of a discrete random variable from a list of outcomes and the probability of each. It returns E(X), the variance, the standard deviation and a table showing what every outcome contributes to each, and a second action carries the same distribution over a number of independent trials to give the expected total and how far it is likely to stray. Probabilities may be typed as decimals adding to 1 or as percentages adding to 100, and either way the total is checked rather than quietly rescaled, because a list that falls short almost always means an outcome was left out. The expected value is a long-run average and usually is not a result the variable can produce on any single trial, which the page says out loud when that is the case.