Tuesday, May 25, 2010

Probability concepts and Probability theorems

Probability concepts and probability theorems is an interesting topic to debate with. The word Probability is something which we use on day today conversation.

In everyday life, we come across statements such as
(1) It will probably rain today.
(2) I doubt that he will pass the test.
(3) Most probably, Kavita will stand first in the annual examination.
(4) Chances are high that the prices of diesel will go up.
(5) There is a 50-50 chance of India winning a toss in today’s match.

The words ‘probably’, ‘doubt’, ‘most probably’, ‘chances’, etc., used in the statements above involve an element of uncertainty. For example, in (1), ‘probably rain’ will mean it may rain or may not rain today. We are predicting rain today based on our past experience when it rained under similar conditions.
In the same way probability theorems can also be explained with the following examples.
Question -
Two coins are tossed simultaneously 500 times, and we get
Two heads : 105 times
One head : 275 times
No head : 120 times
Find the probability of occurrence of each of these events.
Answer -
Let us denote the events of getting two heads, one head and no head by E1,
E2 and E3, respectively. So,

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