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.
Q) which of the follwoing 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.
At first I picked A thinking, suppose 10 people comprise 2/3rd of the people who carry NABH and donate blood ---> They donate to 10 people at least ---> those people get NABH as well (now NABH must be infectious otherwise why are Blood banks testing to find whether ppl have NABH or not)
So increase of 10 people --> ~ 10% increase in NABH infected people.
After knowing I picked the wrong answer, my fallacy is probably this:
We don't know the total number of NABH infected cases: it may be 20 or it may be 10 ---> supposing it is 20, then 10 people addition is ---> 2% increase not 10% OR if it is 100 cases of infections ---> then it is 10% ----> % increase may be 2-10% or more ---> this makes the option A to be MAY BE TRUE.
A conclusion MUST BE TRUE ---> D) says the blood supplies will decrease ---> YES because people are disqualified, so less blood is available from all the possible donors.
Please do let me know if I am right. And also, How i may improve in ASSUMPTION CR, I also take around 3:30 mins in medium-tough questions.
The problem with (A) is that the argument does not give us enough information to deduce that.
10% of actual donors will supply NANB contaminated blood. But does that mean that all this blood will be used? What if actually only 50% of the blood from a blood bank is used. Then the actual incidence of disease may increase by only 5% (assuming homogenous distribution).
Also, what if NANB infected people are the ones who need blood most often from blood banks. In that case, we may find very few new cases.
Hence, increase in the incidence of disease is a big jump.
(D) is straight forward. 5% fewer people will be able to donate blood due to new tests and that means reduced supply is an effect of the new test.
In inference questions, simpler is usually better.
For discussions on assumption questions, check my blog:http://www.veritasprep.com/blog/?s=assu ... er&x=0&y=0
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