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vivektripathi
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One of 5 pens is faulty. They are tested one at a time, what 15 Oct 2008, 05:58
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One of 5 pens is faulty. They are tested one at a time, what is the probability that the faulty pen is :
(a) 1th first one tested (b) the 2nd one testedt
(b) the rd one tested (d) the last one tested



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GMAT TIGER
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One of 5 pens is faulty. They are tested one at a time, what 15 Oct 2008, 14:32
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vivektripathi
One of 5 pens is faulty. They are tested one at a time, what is the probability that the faulty pen is :

(a) 1th first one tested (b) the 2nd one testedt
(b) the 3rd one tested (d) the last one tested
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a) 1/5
b) 1/4
c) 1/3
d) 1

Edit: I supposed no/without repleshment.
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stallone
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One of 5 pens is faulty. They are tested one at a time, what 15 Oct 2008, 16:01
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well :

i get 1/5 for all of them :shock:
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elmagnifico
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One of 5 pens is faulty. They are tested one at a time, what 16 Oct 2008, 08:18
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stallone
well :

i get 1/5 for all of them :shock:
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every time you pick one, the # of total decreases, since no replacement.
so when you pick the second one to be defective there is 1 defective out of 4 total.
when you pick the 3rd to be defective, you have already picked two good one before, so the total should be 3, and 1 of these 3 is defective.
i hope this helps. :lol:
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One of 5 pens is faulty. They are tested one at a time, what 17 Oct 2008, 01:25
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vivektripathi
One of 5 pens is faulty. They are tested one at a time, what is the probability that the faulty pen is :
(a) 1th first one tested (b) the 2nd one testedt
(b) the rd one tested (d) the last one tested
Show more

I am not sure but stem says that there are five pens places I I I I I
1 2 3 4 5
and if pick 1st or 2nd or third or last and test it the probability will remain same i.e. 1/5.



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