1. Probability Distributions

2. 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

3. 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

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

5. 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).

6. 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

7. Page 176
Exercise A
Mean ONLY