Sarah buys a book for her
2 answers:
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Answer:
The value is
Step-by-step explanation:
From the question we are told that
The number of keys is n
The number of keys remaining after the first key is chosen is n-1
The probability that he gains entrance with the first key he selects is
Generally the probability that the first key does not open the door is
Generally the number of keys remaining after the second key is chosen is
n-2
Generally the probability that he gains entrance with the second key he selects is
Generally the probability that the second key does not opens the door is
Generally the probability that he gains entrance with the third key he selects is
Generally the probability that the door opens with the third key
=>
=>
Note :
All the outcome of the events are independent