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Probability

Question
CBSEENMA12033666

Prove that if E and F are independent events,  then so are the events E and F'.

Solution

Since E and F are independent.
∴  P(E ∩ F) = P(E). P(F)
From the Venn diagram in the figure, it is clear that E ∩ F and E ∩ F' are mutually exclusive events and also
           straight E space equals space left parenthesis straight E space intersection space straight F right parenthesis thin space left parenthesis straight E space intersection space straight F apostrophe right parenthesis.
therefore space space space space straight P left parenthesis straight E right parenthesis space equals space straight P left parenthesis straight E intersection straight F right parenthesis space plus space straight P left parenthesis straight E intersection straight F apostrophe right parenthesis
rightwards double arrow space space straight P left parenthesis straight E space intersection space straight F apostrophe right parenthesis space equals space straight P left parenthesis straight E right parenthesis space minus space straight P left parenthesis straight E space intersection space straight F right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space equals space straight P left parenthesis straight E right parenthesis space minus space straight P left parenthesis straight E right parenthesis. space straight P left parenthesis straight F right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
space space space space space space space space space space space space space space space space space space space space space space space space equals space straight P left parenthesis straight E right parenthesis space left square bracket 1 minus space straight P left parenthesis straight F right parenthesis right square bracket
space space space space space space space space space space space space space space space space space space space space space space space space equals space straight P left parenthesis straight E right parenthesis. space straight P left parenthesis straight F apostrophe right parenthesis
∴   E and F' are independent.


Tips: -

Note: In a similar manner, it can be shown that if the events E and F are independent, then
(a)    E' and F are independent,
(b)    E' and F' are independent.

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