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# What is the accurate rate for a certain disease testing? 1).

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Senior Manager
Joined: 05 Jun 2008
Posts: 289
What is the accurate rate for a certain disease testing? 1).  [#permalink]

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20 Sep 2008, 10:56
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What is the accurate rate for a certain disease testing?
1). 96% of the positive results are true, and 90% of the negative results are true.
2). 8% of all people for the testing actually suffered the disease
???

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Manager
Joined: 21 Aug 2008
Posts: 186

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20 Sep 2008, 11:05
vivektripathi wrote:
What is the accurate rate for a certain disease testing?
1). 96% of the positive results are true, and 90% of the negative results are true.
2). 8% of all people for the testing actually suffered the disease
???

C IMO.

From both stem,

8% of all people actually suffered...positive result and true OR negative result but false. So accuracy rate is 96% x 10%.
VP
Joined: 05 Jul 2008
Posts: 1329

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20 Sep 2008, 13:23
Richardson wrote:
vivektripathi wrote:
What is the accurate rate for a certain disease testing?
1). 96% of the positive results are true, and 90% of the negative results are true.
2). 8% of all people for the testing actually suffered the disease
???

C IMO.

From both stem,

8% of all people actually suffered...positive result and true OR negative result but false. So accuracy rate is 96% x 10%.

Where did you get the 10% from ( if you are referring to the negative results that were false) why do you think the answer has to be C?

The wording of B is really ambiguous to me. What does it mean by suffered the disease? They came for testing when they were already knew they had the disease. (or) Does it mean 92% of all the people tested do not suffer the disease. In either case I don't see how it relates to the accuracy of the test.

accuracy = ( true positives + true negatives ) / total cases )

A says

(.96P + .90N) / (P+N)

We dont know P +N

B says

0.08 (X) = P

0.92 (X) = N

Insuff we don't know X

Combine A & B to substitute in terms of X to solve for accuracy.

Initially I picked A but C seems to be the answer. Tough one!
VP
Joined: 17 Jun 2008
Posts: 1279

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20 Sep 2008, 23:19
vivektripathi wrote:
What is the accurate rate for a certain disease testing?
1). 96% of the positive results are true, and 90% of the negative results are true.
2). 8% of all people for the testing actually suffered the disease
???

Whats the source of Question
Looking forward to a solution!!!

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This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Its Now Or Never

Re: DS- Percentages &nbs [#permalink] 20 Sep 2008, 23:19
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