A random variable is name given to a quantity that is capable of taking on different values from trial in an experiment, the exact outcome being a chance or random event. if only certain specified values are possible, the random variable is called a discrete variable. Examples include the number of rooms in a house, the number of people arriving at a supermarket checkout stand in an hour, and the number of defective units in a batch of electronic parts. If any value of the random variable is possible within some range, it is called a continuous variable. Examples of this type of variable are the weights of people, the length of a manufactured part, and the time between car arrivals at a tollbooth