 In decisions under risk, the agent assigns subjective probabilities to the various states of the world. Assume that the states of the world are independent of what the agent does. A figure of merit called the expected utility, or the expectation of a given action can be calculated by a simple formula: for each state, multiply the utility that the action produces in that state by the state’s probability; then, add these numbers. According to decision theory, rationality requires you to perform the action of maximum expected utility (if there is one).