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Preliminary Course in Quantitative
Methods - Lectures III-IV
September 2008
1 Discrete Random Variables
1.1 RANDOM VARIABLE
A random variable associates a numerical value with each outcome of an exper-
iment. A random variable is deÂ…ned mathematically as a real-valued function
deÂ…ned on a sample space, and is represented as a letter such as X or Y.
EXAMPLE: For the experiment of ‡ipping a coin twice, the random variable X
is deÂ…ned to be the number of tails to appear