Probability Distributions

Note 1 : Discrete and Continuous Random Variables A discrete random variable is one which usually takes whole number values. Example: The number of seeds germinating A continuous random variable is one which can take any real value in an interval. Example: The length of a moro bar

Classify each of the following random variables as either discrete or continuous X = the number of heads that occur when ten coins are tossed X = the number of telephone calls that are put through a switchboard in a 5-minute period X = the length of a piece of twine, chosen at random from packets on a supermarket shelf X = the daily power consumption of a heater X = the weight of an egg selected at random from a hen-house

Give an example of two random variables associated with this classroom: Discrete * Continuous

Note 2 : Expected Value The expected value of a random variable is a kind of theoretical average that it should take. The symbol is E(X).

Example: Calculate the expected number of heads if you toss a coin twice. x = number of heads x can take the values 0, 1, and 2 E(X) = 0 x ¼ + 1 x ½ + 2 x ¼ = 1

Page 176 Exercise A Mean ONLY