Means

• Mean: the average value of a data set
• Median: the middle of a data set, the number that splits a data set in two; requires sorting; median of an even number of elements is the mean of the middle two elements
• Mode: value in a data set that occurs most often; if a data set has unique numbers there is no mode; if there are equal numbers of some elements there are multiple modes

Random variables

• Discrete: finite numbers of values
• Continuous: infinite number of values

Probability density functions

P(|Y - 2| < .1) is equivalent to P(1.9 < Y < 2.1)

• Probability is the area under the PDF
• Integral of f(x)d from zero to infinity is 1