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# A certain airport security scanner designed to detect explosives in lu

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Math Expert
Joined: 02 Sep 2009
Posts: 56263
A certain airport security scanner designed to detect explosives in lu  [#permalink]

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03 Jul 2018, 11:15
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Difficulty:

75% (hard)

Question Stats:

47% (01:41) correct 53% (01:52) wrong based on 127 sessions

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A certain airport security scanner designed to detect explosives in luggage will alert the scanner’s operator whenever the piece of luggage passing under the scanner contains an explosive. The scanner will erroneously alert the operator for only one percent of the pieces of luggage that contain no explosives. Thus in ninety‑nine out of a hundred alerts explosives will actually be present.

The reasoning in the argument is flawed because the argument

(A) ignores the possibility of the scanner’s failing to signal an alert when the luggage does contain an explosive

(B) draws a general conclusion about reliability on the basis of a sample that is likely to be biased

(C) ignores the possibility of human error on the part of the scanner’s operator once the scanner has alerted him or her

(D) fails to acknowledge the possibility that the scanner will not be equally sensitive to all kinds of explosives

(E) substitutes one group for a different group in the statement of a percentage

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Re: A certain airport security scanner designed to detect explosives in lu  [#permalink]

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03 Jul 2018, 11:29
Answer is E? Incorrectly comparing no. Of erroneous alerts with no. Of pieces of luggage with no explosives

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Re: A certain airport security scanner designed to detect explosives in lu  [#permalink]

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03 Jul 2018, 11:43
gilltaurus wrote:
Answer is E? Incorrectly comparing no. Of erroneous alerts with no. Of pieces of luggage with no explosives

Sent from my iPhone using GMAT Club Forum mobile app

With the same opinion, must be (E)

Quote:
A certain airport security scanner designed to detect explosives in luggage will alert the scanner’s operator whenever the piece of luggage passing under the scanner contains an explosive. The scanner will erroneously alert the operator for only one percent of the pieces of luggage that contain no explosives. Thus in ninety‑nine out of a hundred alerts explosives will actually be present.

Compares percentage error in one statement to the actual number of alerts !!
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Joined: 07 Dec 2017
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Re: A certain airport security scanner designed to detect explosives in lu  [#permalink]

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10 Jul 2018, 18:59

This is how: acc to the premise, the scanner will show 1% of false positive for all non-explosive luggage

Let's take nos: 100 non-explosive pieces of luggage, the scanner will result in 1 case of False positive but based
on this information, we cant deduce the accuracy for all the luggage which contain explosives as we have
info available for the accuracy of false + for non-explosive Luggage
Re: A certain airport security scanner designed to detect explosives in lu   [#permalink] 10 Jul 2018, 18:59
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