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

Question

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.

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.

KarishmaB · Accepted Answer

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 out these videos: https://youtu.be/O0ROJfljRLU https://youtu.be/ZQnhC4d5ODU

egmat · Answer

Hey  nazii ,

I can help with this one! 
 
This is a question that really tests us on our ability to visualize sentences (this is particularly true of the answer choices!). 
 
 Here  is a video I made that may help provide clarity.

Hope this helps! 
Harsha

teaserbae · Answer

AjiteshArun   ChiranjeevSingh   VeritasKarishma   aragonn 
As per the question 
Let's assume there are 100 people who donate blood
now 15 have NANB hepatitis 5 are removed from the screening. So 10 are left
Conclusion: Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood. 
It means the 5 people which are removed are replaced by new donors free from NANB hepatits
So how can we inder D ? since the donors remain the same
What's the flaw in my reasoning ?

KarishmaB · Answer

There is a problem in the highlighted sentence. How do you figure that they will be replaced by new donors? The argument says "5 percent of all prospective blood donors will be disqualified"
From where will the new donors come?

ballest127 · Answer

Hi Experts,

I have doubt on D.

Can we readily assume that there will no significantly more people that would like to donate blood?
If it is not the case, the blood supply can still increase.

Please explain.

Thank you.

GMATNinja · Answer

The question states, "Which of the following inferences about the consequences of instituting the new tests is   best supported   by the passage above?" So we don't need to PROVE that (D) is true; as long as the information in the passage supports (D) more than any other choice, we've found our winner. And by POE, we can see that (D) is the best bet.

Also, notice the wording of (D) itself: "The blood supplies available from blood banks are   likely   to go down." (D) does not say the blood supplies will DEFINITELY go down. The passage  suggests  that blood supplies will probably go down, so (D) is spot on.

I hope that helps!

akbgmatter · Answer

A) The incidence of new cases of NANB hepatitis is likely to go up by 10 percent.
Relationship between donors with NANB and cases isn't given; May be 10 % is utilized by 2%?; Eliminate

B) Donations made by patients specifically for their own use are likely to become less frequent.
Irrelevant; Eliminate

C) The demand for blood from blood banks is likely to fluctuate more strongly.
Fluctuate means go up, down or both. While the demand can go up due to shortage caused by disqualification of 5% donors, other options can't be consequences of the new test. Eliminate.

D) The blood supplies available from blood banks are likely to go down.
Solid option, if the donors go down, then the supplies will go down. Hold.

E) The number of prospective first-time donors is likely to go up by 5 percent.
Goes too far; Eliminate.

D wins!

nazii · Answer

@e gmat 
would you pls help I can't understand at all

nazii · Answer

I appreciate you billion times

It was very helpful it is the best explanation ever on this question I love egmat

Raman109 · Answer

Inference-based question - so let's jump to the option elimination -

A) The incidence of new cases of NANB hepatitis is likely to go up by 10 percent. - We don't know. How about if earlier, all these 15% were donating, but now the 5% are filtered at the source, so the cases should actually go down? So, it may or may not be true. Such options are not true on Inference.

B) Donations made by patients specifically for their own use are likely to become less frequent. - Is there anything like this mentioned in the passage (In inference questions no new information please, we have to stick to the argument). Out of scope.

C) The demand for blood from blood banks is likely to fluctuate more strongly. - We don't know. The argument just talks about the supply side of the equation. Anything mentioned on the demand side? No. Out of scope.

D) The blood supplies available from blood banks are likely to go down. - Perfect. Earlier suppose 100 blood brackets were in the blood bank. Now 95. Number decreased.

E) The number of prospective first-time donors is likely to go up by 5 percent. - Do we know anything about first-time donors from the argument? No. Out of scope.

MrMBB · Answer

I chose option D because 
let x be infected donor and y be total donor. x/3 =y/20(as 55 of actual donor is equal 1/3 of infected donor so from here we get infected donor now constitute 15% of actual donor. Now once the 1/3 of infected donor are qualified the 2/3 of infected donor should be more than 10 % of actual donor as actual donor has decreased.but it remains the same which means the total do or must have remained same. So fulfil the gap the number of 1st time donor must be up by 5% of current actual donor.

siddhantvarma · Answer

New Screening: All donors will be tested for NANB hepatitis.

Disqualification Rate: The new test will disqualify up to 5% of all prospective blood donors.

Test Accuracy: The test still misses two-thirds of the donors who actually have NANB hepatitis, so only one-third of infected donors get caught.

Result: 10% of Actual Donors Are Contaminated
Because up to 5% are disqualified (one-third of those who are infected), the remaining two-thirds of infected donors—about 10% of the total donor pool—will still donate contaminated blood.

What the Passage Doesn't Tell Us
- Nothing about demand for blood.
- Nothing about first-time donors or autologous (self-use) donations.
- Nothing about the amount of blood each donor contributes

A) The incidence of new cases of NANB hepatitis is likely to go up by 10 percent. 
The 10% statistic refers to the fraction of donors with infected blood, not the percentage increase in disease in the overall population.
Moreover, screening out 5% of infected donors could reduce the incidence, or it might have no net effect—there’s insufficient information.

B) Donations made by patients specifically for their own use are likely to become less frequent. 
The passage doesn’t mention autologous donations or how frequently such patients donate.

C) The demand for blood from blood banks is likely to fluctuate more strongly. 
The passage discusses supply (donors and screening), not demand (how many people need blood).

D) The blood supplies available from blood banks are likely to go down. 
Because up to 5% of would-be donors are disqualified, the supply of donated blood is likely to decrease.
The word “likely” is important because we are not certain how often non-disqualified donors might donate or how large their donations are. Still, disqualifying donors generally lowers potential supply.
Best supported choice.

E) The number of prospective first-time donors is likely to go up by 5 percent. 
No information suggests more people will start donating. The passage only states that 5% get disqualified, not that new donors will appear.
Not supported by the passage.

Answer: (D)

agrasan · Answer

Hi experts  GMATNinja   KarishmaB   MartyMurray   IanStewart

I needed some time to simplify complex data given in the argument " 5 percent of all prospective....they will still miss two-thirds of donors carrying NANB hepatitis", however, I understood that there will be supply issues for pure blood likely according to the conclusion.

I wanted to check if above is correct approach for inference questions or I should still have illustrative figures in my mind and then only mark the correct option?

Please let me know your thoughts.

DmitryFarber · Answer

That's a tough balance to strike. We might work out a lot of quantitative details, only to find that the answer doesn't rely on that! I'd say that if you can quickly and easily draw some conclusions before looking at the answers, you should do so. In my case, I concluded that if we're going to miss 2/3 of cases, and that leads to a 10% rate of contamination in the supply, then 15% of donors have NANB. (We might have come to a similar conclusion from the 5%. If catching 1/3 of cases leads to the disqualification of up to 5% of donors, then up to 15% of donors have NANB.) However, that wasn't in any of the answers. I don't feel bad, since the conclusion didn't take me long, but I'd say to spend no more than about 30 seconds on that part.

We can't actually infer D from the last line (and that line is not really a conclusion in the normal sense). That just tells us that some of the blood will still be contaminated, but this is blood that PASSES testing, so it's in the supply! The proof of D is in the 5% that we will screen out.

KarishmaB · Answer

This question does not test your understanding of the given figures since it is readily given that 5% people will be disqualified in future. So you know that blood supply is likely to reduce (assuming all else remains same). But in such questions, usually inferences are based on your understanding of the relations between the given figures and what you can infer from them. I would suggest you to take some time to understand this. Keep in mind, the 3 sections of GMAT are all interlinked - you will find percentages, w avgs and sets in CR too.

anindhio · Answer

Hi  KarishmaB

I picked D for the answer but could you please confirm my reasoning on D:

Since it is mentioned that 2/3 still miss of donors carrying the hepaitis, and based on D the supply is lower and hence the blood supply that is contaminated with hepatitis that isn't filtered from the test is bigger. Hence people will have bigger chance of getting that contaminated blood.

and also the reason why I rejected A is because the answer choice only tells that the incident of hepatitis increased by 10%, but we don't know whether this people will contribute to the donor or no

KarishmaB · Answer

I am not sure I am clear on the reason you have mentioned.

This is the scenario without NANB testing:  
100 people donate.
15 have NANB.
All 100 is used.
So there is a 15% chance that someone will get NANB if they are using the blood.

NANB screening comes in.  
100 people donate.
15 have NANB.
Screening happens and 5 units are removed (1/3rd are found and removed).
Now 95 are available to be used. Of these 10 still have NNAB. 
There is a 10/95 = 10.5% chance that someone will get NANB if they are using the blood.

What do we know for sure?

That less blood is available now. Only 95 units, not 100. So (D) works.

(A)  The incidence of new cases of NANB hepatitis is likely to go up by 10 percent.

No info on this. Will the incidence of new NANB cases increase by 10% because about 10% of the blood is infected? We don't know. 
The incidence of new NANB cases depends on how many non NANB infected people and current NANB infected people use the infected blood.

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

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

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615 to 715 in 15 Days (Ria's Strategies)

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