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.

19. 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.

20. Which of the following inferences about the consequences of instituting the new tests is best supported by the passage above?
(A) The incidence of new cases of NANB hepatitis is likely to go up by 10 percent.
(B) Donations made by patients specifically for their own use are likely to become less frequent.
(C) The demand for blood from blood banks is likely to fluctuate more strongly.
(D) The blood supplies available from blood banks are likely to go down.
(E) The number of prospective first-time donors is likely to go up by 5 percent.

A for 19 and D for 20.

the argument says that

about 10 percent of actual donors will still supply NANB-contaminated blood.. This means that it assumes that these 10% people will not be rendered unfit because of some other reason.
So, A should be the answer to Q-19.

D sounds like the only right choice for 20.
_________________

for every person who doesn't try because he is
afraid of loosing , there is another person who
keeps making mistakes and succeeds..

Mine is 'A' and 'D'

Post the OA please.

Use numbers to attack this CR. Lets say there are 100 total donors. Lets say the screening eliminates 5 donors(equal to 5% rate quoted in the argument). Therefore, there are 95 donors left. The passage says that the initial screening only eliminates 1/3rd of NANB patients. If that is true then,

1/3 of NANB patients = 5 donors

Implying,

Total number of NANB patients = 3*5=15

Out of this 15-5=10 patients were undetected by the screening. But does that mean they will definitely donate blood. For them to donate blood, they need to pass through all the other screening tests or in other words, their infection should not be detected through other routinely conducted tests.

Paraphrase this reasoning and you get (A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

Is this helpful?

Thanks guys for the explanation...........i got confused with the number.......now its very clear