This is only true if A and B are independent. You can never assume A and B are independent. You must either know it or prove it.

This is always true for two events A and B. The left hand side P(A divides B) is the probability that A will happen given that B has happened, often written as A given B or A conditional on B. If A and B are independent thenso

This is always true.

The above equations are very useful when working with Venn diagrams.

Correlation Coefficients and Regression Lines

where

If the equation of a regression line ofonis given bythenand

The unbiased estimate of the standard deviation of a random variablefound from a list of n numbersis given bywhere

If the expectation value – often called the mean, average, and writtenor– of a random variableis given byandthen

and

andfor all distributions, but if the distribution is continuous we may useand

andfor a continuous distribution etc.

for a continuous distribution.