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18 Apr 2018, 18:23
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
73% (00:47) correct
27%
(01:17)
wrong
based on 194
sessions
History
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Only one of ten pens in a box is defective. Three pens are randomly drawn from the box, one at a time. If none of those three pens is defective, what is the probability that the next pen randomly drawn is defective?
(A) 1/10
(B) 1/7
(C) 7/10
(D) 6/7
(E) 9/10
(A) 1/10
(B) 1/7
(C) 7/10
(D) 6/7
(E) 9/10
18 Apr 2018, 19:11
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Was: 9 non-defective + 1 defective = 10
Minus: 3 non-defective
Now: 6 non defective + 1 defective = 7
Probability to get 1 defective = 1/7
Answer (B) 1/7
Minus: 3 non-defective
Now: 6 non defective + 1 defective = 7
Probability to get 1 defective = 1/7
Answer (B) 1/7
19 Apr 2018, 12:27
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I think it might help to have the information whether the pen drawn is put back into the box. That is, are the events independent?
