Blood banks will shortly start to screen all donors for NANB : GMAT Critical Reasoning (CR)
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# Blood banks will shortly start to screen all donors for NANB

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

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09 Mar 2011, 19:18
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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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Re: Blood banks will shortly start to screen all donors [#permalink]

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10 Mar 2011, 03:18
assumption : there will not be a external factor reducing the available donors. That's A

dips 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.
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Re: Blood banks will shortly start to screen all donors [#permalink]

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20 Mar 2011, 03:32
Answer - A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed

So they'll escape the screening here, and the other screenings also, hence the number of infected donors who did not get filtered out does not change.

Say there are 15% donors affected, so 2/3 * 15 escape, hence 10% remain, they don't get caught in any other test so the %age is constant.
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Re: Blood banks will shortly start to screen all donors for NANB [#permalink]

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14 Nov 2014, 23:49
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Re: Blood banks will shortly start to screen all donors for NANB [#permalink]

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14 Nov 2015, 06:47
(1) For example, we have 300 people prospective donors;

(2) 5% of donors (15 people) were disqualified, the remaining number of donors is 285;

(3) 2/3 of remaining donors which are 190 people with NANB hepatitis

(4) conclusion says that 10% of (screened) donors which is 30 people still have NANB hepatitis

Can YOU please explain me where is consistency of 190 people (2/3) with 30 people (10%)?
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Blood banks will shortly start to screen all donors for NANB [#permalink]

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16 Nov 2015, 20:08
ziyavutdinov wrote:
(1) For example, we have 300 people prospective donors;

(2) 5% of donors (15 people) were disqualified, the remaining number of donors is 285;

(3) 2/3 of remaining donors which are 190 people with NANB hepatitis

(4) conclusion says that 10% of (screened) donors which is 30 people still have NANB hepatitis

Can YOU please explain me where is consistency of 190 people (2/3) with 30 people (10%)?

The stem states that 5% of all donors will be screened out, i.e. 15 in your case. However, they will still miss 2/3s of donors carrying NANB hepatitis. This means, that the 15 donors captured by the screen only account for 1/3 of donors carrying NANB hepatitis. Well, if that's the case, then there should be 30 donors, i.e. 10% of 300, to go undetected by the screen.

Your third step should be 15 people x 3 = 45 = 15% of 300.
Blood banks will shortly start to screen all donors for NANB   [#permalink] 16 Nov 2015, 20:08
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