For what percent of those tested for a certain infection was

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For what percent of those tested for a certain infection was [#permalink]

04 Feb 2006, 17:13

For what percent of those tested for a certain infection was the test accurate; that is, positive for those who had the infection and negative for those who did not have the infection?

1) of those who tested positive for the infection, 1/8 did not have the infection

2) of those tested for the infection, 90% tested negative

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05 Feb 2006, 12:59

willget800 wrote:

E not suff..

we need to know the total number.... which is not given... so E
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05 Feb 2006, 19:12

hmmmm . A says that for people who tested positive, 1/8 didnt have the infection.

Doesnt that mean that 7/8 actually did ?

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05 Feb 2006, 20:10

Total tested = a
Positive = b

1) 7b/8 accurate -> percentage = 7 b/8a * 100%. Insufficient.

2) We only know 90% tested negative but not the actual figure who are really negative. Insufficient.

1) and 2):

Assume total tested = 100
Positive = 10
Negative = 90

Positive percentage = 7/8 * 10 * 100% -> accuracy for those tested postiive
Negative percentage = ??

Insufficient.

Ans E

[#permalink] 05 Feb 2006, 20:10

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For what percent of those tested for a certain infection was

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For what percent of those tested for a certain infection was

For what percent of those tested for a certain infection was

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