Statistics And Probability Question 113

Question: The odds against a certain event is 5 : 2 and the odds in favour of another event is 6 : 5. If both the events are independent, then the probability that at least one of the events will happen is

[RPET 1997]

Options:

A) $ \frac{50}{77} $

B) $ \frac{52}{77} $

C) $ \frac{25}{88} $

D) $ \frac{63}{88} $

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Answer:

Correct Answer: B

Solution:

  •                 Let                                                                                                      $ A $   and                                                                                                      $ B $   be two given events. The odds against                                                                                                      $ A $   are  $ 5:2 $ , therefore                                                                                        $ P(A)=\frac{2}{7} $  .                    The odds in favour of                                                                                                      $ B $   are  $ 6:5 $ ,                    therefore                                                                                       $ P(B)=\frac{6}{11}. $                     The required probability                                                                                 $ =1-P(\bar{A})\,P(\bar{B}) $                                                                                                                      $ =1-( 1-\frac{2}{7} )\,( 1-\frac{6}{11} )=\frac{52}{77}. $