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# Blood banks will shortly start to screen all donors for NANB

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Director
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Blood banks will shortly start to screen all donors for NANB [#permalink]

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06 May 2008, 07:10
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Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.
The argument above depends on which of the following assumptions?

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.
(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

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Manager
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Re: CR - blood bank [#permalink]

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06 May 2008, 07:21
saravalli wrote:
Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.
The argument above depends on which of the following assumptions?

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.
(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

I get E.
A and B - irrelevant.
C - underestimate ? how?
D - argument doesn't mentions about population at large.

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Director
Joined: 26 Jul 2007
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Schools: Stern, McCombs, Marshall, Wharton
Re: CR - blood bank [#permalink]

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06 May 2008, 07:30
E

"Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis."

This statement tells us that 15% of prospective blood donors have hepatitis and one third will be detected by the screening. 10% of prospective blood donors who can still donate.

"Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood."

The conclusion is that 10% of actual donors will have hepatitis.

To reach that conclusion we must assume that the infected prospective blood donors will become actual donors at the same rate that non infected donors will.

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Manager
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Re: CR - blood bank [#permalink]

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06 May 2008, 08:23
saravalli wrote:
Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.
The argument above depends on which of the following assumptions?

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.
(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

None of the answers really stood out to me - but at the end I just chose D, beacuse I felt there should be some connection between 'actual' and prospective' donors and felt that D did that with 'potential blood donors' and 'population at large'

gixxer,

I understood your analysis until the end - can you clarify how the rate/frequency could affect the outcome? I feel the 5% and 10% number is an absolute number so whether that number of affected donors donate at the beginning, middle, or end of the donation period should not matter.
Either way, at the end of the day, 5% are disqualified and 10% are not detected.

Thanks.

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Director
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Re: CR - blood bank [#permalink]

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06 May 2008, 08:37
gmat blows wrote:

None of the answers really stood out to me - but at the end I just chose D, beacuse I felt there should be some connection between 'actual' and prospective' donors and felt that D did that with 'potential blood donors' and 'population at large'

gixxer,

I understood your analysis until the end - can you clarify how the rate/frequency could affect the outcome? I feel the 5% and 10% number is an absolute number so whether that number of affected donors donate at the beginning, middle, or end of the donation period should not matter.
Either way, at the end of the day, 5% are disqualified and 10% are not detected.

Thanks.

Sure gmatblows,

You just have to recognize the difference between prospective and actual.

ex. 100 people are prospective donors. 15% or 15 have hepatitis. The screening detects one third or 5 of them, leaving 10 prospective infected donors.

So we have 10 prospective infected donors out of 95 total eligible donors. The 10 infected donars make up 10.5%. But what if 4 of those prospective donors choose not to donate and all of the non-infected donors do. Then you would have 6 infected and 95 non infected and the actual percentage of infected donors would change to about 6%. The same thing in reverse if only 60 of the potential non-infected donors became actual donors along with all 10 infected donor then the percentage would change to about 17%.

So the potential infected and non-infected donors must become actual donors at the same rate.

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Re: CR - blood bank [#permalink]

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06 May 2008, 14:03
I vote for A.

For the Q minded folks, another way of looking at this CR.

11-p341982?t=48587&hilit=+NANB#p341982

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Director
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Kudos [?]: 180 [0], given: 0

Schools: Stern, McCombs, Marshall, Wharton
Re: CR - blood bank [#permalink]

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06 May 2008, 14:20
I vote for A.

For the Q minded folks, another way of looking at this CR.

http://www.gmatclub.com/forum/11-p34198 ... NB#p341982

Wow! I looked at the other explanations and I really disagree.

Under that same logic we would also have to assume that the non-infected donors also do not carry other infections for which reliable screening tests are routinely performed. The number of actual prospective infected and non-infected donors that become actual donors is what we have to assume to reach 10% conclusion. If either side doesn't convert at the same rate then the conclusion fall apart.

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Manager
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Re: CR - blood bank [#permalink]

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07 May 2008, 08:18
gixxer1000 wrote:
gmat blows wrote:

None of the answers really stood out to me - but at the end I just chose D, beacuse I felt there should be some connection between 'actual' and prospective' donors and felt that D did that with 'potential blood donors' and 'population at large'

gixxer,

I understood your analysis until the end - can you clarify how the rate/frequency could affect the outcome? I feel the 5% and 10% number is an absolute number so whether that number of affected donors donate at the beginning, middle, or end of the donation period should not matter.
Either way, at the end of the day, 5% are disqualified and 10% are not detected.

Thanks.

Sure gmatblows,

You just have to recognize the difference between prospective and actual.

ex. 100 people are prospective donors. 15% or 15 have hepatitis. The screening detects one third or 5 of them, leaving 10 prospective infected donors.

So we have 10 prospective infected donors out of 95 total eligible donors. The 10 infected donars make up 10.5%. But what if 4 of those prospective donors choose not to donate and all of the non-infected donors do. Then you would have 6 infected and 95 non infected and the actual percentage of infected donors would change to about 6%. The same thing in reverse if only 60 of the potential non-infected donors became actual donors along with all 10 infected donor then the percentage would change to about 17%.

So the potential infected and non-infected donors must become actual donors at the same rate.

gracias gixxer - makes a whole lot more sense!

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Current Student
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Re: CR - blood bank [#permalink]

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07 May 2008, 08:22
i say A..the assumption is that theses contaminated donors cannot be caugt by the screeining..well what if contaminated donors also have some other disease that can be detected? then the conlusion falls apart.

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Manager
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Re: CR - blood bank [#permalink]

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07 May 2008, 08:35
saravalli wrote:
Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.
The argument above depends on which of the following assumptions?

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.
(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.
>> out of the scope.
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.
>> We do not know this.
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.
>> Out of the scope.
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.
>> The argument is nothing to do with the frequency of donation.

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Manager
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Re: CR - blood bank [#permalink]

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07 May 2008, 08:48
gixxer1000 wrote:
I vote for A.

For the Q minded folks, another way of looking at this CR.

http://www.gmatclub.com/forum/11-p34198 ... NB#p341982

Wow! I looked at the other explanations and I really disagree.

Under that same logic we would also have to assume that the non-infected donors also do not carry other infections for which reliable screening tests are routinely performed. The number of actual prospective infected and non-infected donors that become actual donors is what we have to assume to reach 10% conclusion. If either side doesn't convert at the same rate then the conclusion fall apart.

I just had a chance to take a look at the other discussion, and although I agree that the frequnecy that infected and non-infected donate must be at the same rate, I think that factor is considered into A) when it says, 'in a large percentage of cases'

so, although there may be some instances in which the results may vary due to the inconsistency you had mentioned, by using a large pool such inconsistency may become insignificant.

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Re: CR - blood bank [#permalink]

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07 May 2008, 21:59
A
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Check out the new Career Forum
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Re: CR - blood bank [#permalink]

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08 May 2008, 00:32
gixxer1000 wrote:
gmat blows wrote:

None of the answers really stood out to me - but at the end I just chose D, beacuse I felt there should be some connection between 'actual' and prospective' donors and felt that D did that with 'potential blood donors' and 'population at large'

gixxer,

I understood your analysis until the end - can you clarify how the rate/frequency could affect the outcome? I feel the 5% and 10% number is an absolute number so whether that number of affected donors donate at the beginning, middle, or end of the donation period should not matter.
Either way, at the end of the day, 5% are disqualified and 10% are not detected.

Thanks.

Sure gmatblows,

You just have to recognize the difference between prospective and actual.

ex. 100 people are prospective donors. 15% or 15 have hepatitis. The screening detects one third or 5 of them, leaving 10 prospective infected donors.

So we have 10 prospective infected donors out of 95 total eligible donors. The 10 infected donars make up 10.5%. But what if 4 of those prospective donors choose not to donate and all of the non-infected donors do. Then you would have 6 infected and 95 non infected and the actual percentage of infected donors would change to about 6%. The same thing in reverse if only 60 of the potential non-infected donors became actual donors along with all 10 infected donor then the percentage would change to about 17%.

So the potential infected and non-infected donors must become actual donors at the same rate.

gixxer,
your reasoning seems very strong! But I lost in this pile. Sorry! Can you use formula or separate it step by step!

1. I dont know from where you take 15% or 15? that is a freely take, or it come from the original! I dig the origin sentence, no have.

2. Honestly, I stuck at every percentage question!

Thanks!
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Director
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Re: CR - blood bank [#permalink]

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08 May 2008, 06:31
OA: A Thanks guys

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Re: CR - blood bank   [#permalink] 08 May 2008, 06:31
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# Blood banks will shortly start to screen all donors for NANB

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