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Probability of an Event

Rule: The probability of an event A is calculated by summing the probabilities of the sample points in the sample space for A.

 

Classical definition of probability. If an experiment may lead to one and only one of n different equal outcomes and m is a number of favorable outcomes for occurrence of event A then the probability of event A can be calculated by formula

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In other words, the probability of an event A is calculated by summing the probabilities of the sample points in the sample space for A.

Example Take the sample space S for four tosses of a coin to be the 16 possible outcomes in the form HTHH. Then exactly 2 heads is an event. Call this event A. The event A expressed as a subset of outcomes is

A = {HHTT, HTHT, HTTH, THHT, THTH, TTHH}

P(A)=P({HHTT, HTHT, HTTH, THHT, THTH, TTHH})

=P({HHTT})+P({HTHT})+P({HTTH})+P({THHT})+P({THTH})+P({TTHH})= 6/16=3/8


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  1. The Most important events in the 20th centuries.




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