A chemical company claims that, since only one of 520 rats that were

Question

A chemical company claims that, since only one of 520 rats that were given high doses of a new artificial sweetener developed cancer while all the others remained healthy, the sweetener is not carcinogenic for human beings and ought to be approved for human consumption.

Which of the following, if true, most strongly supports the chemical company’s claim?

(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.

(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.

(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.

(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.

(E) The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old.

IanStewart · Accepted Answer

jainu - you're reading far too much into answer D. It says that *certain* (i.e. 'some', not 'all') substances which are carcinogenic for humans are not carcinogenic for rats. That means that some substances which are carcinogenic for humans *are* also carcinogenic for rats. In any case, if there were no relationship between rats and humans, the study in the passage would be completely pointless, and wouldn't prove anything about whether the sweetener was dangerous for humans, so D would weaken the argument.

The answer should be B - if 1 in 540 rats will develop cancer spontaneously, statistically you'd expect one of the rats in the study to develop cancer whether given the sweetener or not. This suggests that the sweetener may not have caused a single case of cancer, strengthening the claim that the sweetener is "not carcinogenic". If we didn't have this information, and if the one cancer from the study were indeed attributable to the sweetener, then clearly the sweetener *is* carcinogenic, at least in a small proportion of cases. For the company to make the rather extreme claim that the sweetener is "not carcinogenic", it must be able to establish that the sweetener is not responsible for a single case of cancer, so we need an answer choice which provides an alternative explanation for the one observed case of cancer in the study.

IanStewart · Answer

The argument says, essentially:

We tested our sweetener on rats, and one rat got cancer. Therefore our sweetener does not cause cancer.

That should seem like a baffling argument, on first read. The conclusion seems to contradict the evidence. It is only a good argument if we have a better explanation, different from the sweetener, for the one observed case of cancer. And if it would be normal, when 500 rats do not consume the sweetener, for one of them to get cancer, then the experiment's results are exactly what you'd expect if the sweetener does not cause cancer. If the sweetener did cause cancer, you'd expect more than 1 out of 500 rats to get cancer after taking it. That's why we care a lot here about the 'spontaneous incidence' of cancer among rats in this question.

The logical issue tested here is actually topical right now. If, after one million vaccine shots are administered, three people experience some health effect, there's no way to know if that's alarming or normal unless we know how many people would experience that same health effect without vaccination. Just because one thing happens after another does not mean the first thing caused the second -- that's the "post hoc ergo propter hoc" fallacy in logic.

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buffdaddy · Answer

Conclusion here is that the sweetner will not cause cancer in humans since only 1/520 rats got cancer in a trial on 520 rats. The questions asks what will support this.

walker · Answer

B

A chemical comp claims that, since only one of 520 rats that were given high doses of a new artificial sweetner developed cancer while all the others remained healthy, the sweetner is not carcinogenic for human beings and ought to be approved for consumption for human consumption.

Which of the following, if true, most strongly supports the chemical company's claim?

the first assumption: one of 520 is not carcinogenic.
the second assumption: not carcinogenic for rats means not carcinogenic for human.

(A)Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.
 irrelevant.Two flaws: "animals" instead of "human", "carcinogenic" instead of "not carcinogenic".

(B)The spontaneous incidence of cancer in this particular strain of rat is approx one in 540.
 it is the first assumption.

(C)Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetner similar to that of rats, 53 developed cancer.
 irrelevant. Is 53 of 500 normal?

(D)Certan chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.
 weaken

(E)The average lifespan of the strain of rat used in the experiment when the rats wrer 13 months old.
 irrelevant.

jainu · Answer

i think D because if it is proved that chemicals carcinogenic for humans are not carcinogenic for rats. This means that carcinogens for humans are exclusive to carcinogens for rats. That is there is no common chemical that can be carcinogenic for both. Hence chemicals that have been found in arg to be carcinogenic for rats are not carcinogenic for humans. Hence can be approved. 
Also,
  If carcogenic for humans  --->  not carcogenic for rats 
reverse the relation.... Carcogenic for rats  ----->  not carcogenic for humans. So clealry D 
So D

mSKR · Answer

B. How B is irrelevant , we don’t care about spontaneous. What if cancer incidence happens later
C . so if it is 53 in some strain of rat then it can be dangerous for humans also
D. it weakens the claim . it maybe possible that whatever doesn’t appear in rat experiments, it may happen to humans. too risky
E. So It means the experiment was not completed
I chose A because if something happen to rats then it happens to other animals. So chances are it happens to humans also. In other side, if something doesn’t happen to rats, it may not happen to animals and thus may not happen to humans.
That’s why I chose A
But I find I am too far from correct

VeritasKarishma   IanStewart   DmitryFarber   BrentGMATPrepNow   CrackVerbalGMAT   EducationAisle   vv65 : what am I missing in understanding the argument.

thanks!

vv65 · Answer

I was about to explain by using the example of Covid-19 vaccines, but IanStewart has done that already

The right answer will show that if only 1 of the 520 rats got cancer, that is good news. The right answer will make the statement "the sweetener is not carcinogenic for humans" more believable. Spontaneous means "happening without apparent external cause; self-generated" What Answer choice B means: for this type of rat, 1 in 540 rats usually get cancer anyway . In a test of whether the sweetener is harmful, we can expect 1 in 540 rats to get cancer. Suppose 50 rats in the group had developed cancer, it would have been worrying. But 1 in 520 is not cause for worry. About your question "What if cancer incidence happens later?" It is true that we do not know how long the testers waited to see the effects of the sweetener. Obviously, if they waited (say) only two days, that is too short and cancer could develop later. But we cannot assume that they did not wait long enough. In the absence of other information, we assume that things were done normally. This is irrelevant. It neither strengthens nor weakens the conclusion that the sweetener is not carcinogenic for either rats or humans or any other animals. You said, "if something happen to rats then it happens to other animals." Yes, that is the reason for testing on rats. And the main purpose of testing is to find out whether the sweetener is carcinogenic for rats. Answer Choice A tells us nothing about that. Important to remember: It is possible that the sweetener is carcinogenic despite the info in Answer Choice B. But the right answer of a strengthen question does not need to prove the conclusion beyond any doubt. It just needs to make the conclusion more believable. Hope this helps. Thank you for asking me!

KarishmaB · Answer

mSKR  - Ian has already explained why (B) works so nothing left for me to add on that.

I am giving my analysis of the other options below.

Company's Claim: The sweetener was given to 520 rats and only 1 got cancer. 
Company's Conclusion: The sweetener is not carcinogenic for human beings and ought to be approved for 
human consumption.

There are multiple things I need to know before I can say whether the company's claim is valid:

1. Do rats normally get cancer? If no, then why did that 1 rat get it? Perhaps the sweetener is carcinogenic then. If yes, what is the normal rate of occurrence in rats? If 1 in 10,000 rats get cancer then the sweetener may have had a bad effect. If 1 in 20 rats get cancer then the sweetener may actually be acting as anti-cancer! If 1 in 500 rats gets cancer then it seems the sweetener has no link to cancer. 
2. Do human beings also experience the same effect of chemicals as do rats? If yes, then it seems the company's conclusion is justified. If no, then perhaps the company's conclusion is not justified.

We need something that supports the company's claim i.e. something that says that the sweetener is not carcinogenic.

(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.

This tells us that other animals used in experiments also experience effects similar to rats. But what about humans? How similar or different their reactions are? The similarity between all animals that are experimented on is irrelevant to us. We need to know the differences/similarity between those animals and humans.

(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.

Correct. As discussed above, we were looking for this information. If naturally 1 in 540 rats gets cancer then it looks like the sweetener is not linked to cancer.

(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.

Are mice similar to humans? If they are, then this weakens our conclusion.

(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.

So this says that rats and humans are not very similar. Some chemicals could be carcinogenic in humans even if they are not in rats. Then this weakens the company's conclusion.

(E) The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old.

This again puts a question mark on the company's conclusion. The rats could have developed cancer later. Hence, it doesn't strengthen the conclusion.

Answer (B)

Nina1987 · Answer

GMATNinja , IanStewart , KarishmaB , DmitryFarber , GMATNinjaTwo , MartyTargetTestPrep , ScottTargetTestPrep , RonPurewal , KyleWiddison , DavidTutorexamPAL , MarkSullivan , AjiteshArun , EMPOWERgmatRichC , ThatDudeKnows , ReedArnoldMPREP , mikemcgarry , sayantanc2k , TommyWallach , Testluv , AndrewN wrt B, in the experiment the odds of getting cancer improved from 1/540 to 1/520. don't we need to know if this increase is statistically significant or not? are we allowed an assumption for an assumption?

KarishmaB · Answer

The difference between 1 in 540 and 1 in 520 is negligible. 500 is a big number compared with 1. 
If the stats were 1 is 3 people, then 1 in 4 is significantly different. But since we are talking about 1 in 500, 520 or 540 doesn't make much of a difference. 
In any case, we have no other option that strengthens the claim.

IanStewart · Answer

Say you have 540 rats, exactly one of which will get cancer. You line the rats up and pick the first 520 of them for your experiment. The probability the rat that will get cancer is among the 520 you choose is 520/540 ~ 96.3%.. So it's enormously probable you'll have a rat among your 520 that will spontaneously develop cancer, and you don't need any information about statistical significance.

Raman109 · Answer

Option elimination -

(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.  Other animals are out of scope.

(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540. -  Spontaneous means without external stimulus but even if we don't know what spontaneous means (it's an adjective) it says the incidence of cancer in this strain of rat is 1 in 540, which means that even without this sweetener, 1 in 540 rats develop cancer. It actually strengthens our case.

(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer. -  53 out of 500 is more than 10%. Pretty significant jump from 1 in 520 <0.2% . From 0.2% to 10% raises doubts. At best it is a weakener.

(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats. -  Weakener.

(E) The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old.  Weakener.

MartyMurray · Answer

Good question, and here's the thing.

The passage doesn't say that the probability of cancer in rats is 1 in 520 in the sweetener test batch.

Rather, it say that there were 520 rats in the group, and 1 got cancer.

One rat in a group of 520 could get cancer even if, in general, the probability of rats who have been consuming the sweetener getting cancer is actually 1 in 540.

Meanwhile, if only 1 in 520 got cancer, then we can be pretty sure that rats' eating the sweetener doesn't cause the probability to increase to, say, 1 in 100 or 1 in 10.

So, what choice (B) says about the rate of cancer in rats being 1 in 540 indicates that the fact that 1 rat in the group of 520 got cancer indicates that eating the sweetener doesn't cause a significant change in the rate of cancer in rats.

In other words, choice (B) helps make the argument more convincing by providing a base cancer rate to compare with the 1 in 520 rate seen in the group.

agrasan · Answer

Hi experts  KarishmaB   GMATNinja

I understand why option B is correct but not able to reject option E properly.
"The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old."
My reasoning is if company terminated the experiment 7 months before the average life span of 2yrs then it increases the credibility of the study as it means that there was a sufficient time for the company to observe cancer cases before rates died, thus, increasing my confidence in the chemical company's observation on 520 rats being correct, ultimately conclusion on it not being carcinogenic. Could you please let me know what I am doing wrong here?

napolean92728 · Answer

Answer: B 
The correct answer is (B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.

Explanation: 
The company's claim is that the sweetener is not carcinogenic based on only 1 of 520 rats developing cancer. Option B strongly supports this by revealing that the natural cancer rate in these rats is approximately 1 in 540 without any exposure to the sweetener. This means the observed cancer rate in the experiment (1 in 520) is virtually identical to what would be expected naturally, suggesting the sweetener had no carcinogenic effect at all. This statistical context significantly strengthens the company's argument.

Why each other option is incorrect: 
 (A)  This only establishes that rat studies might predict carcinogenicity in other experimental animals, not humans specifically. It doesn't directly support the company's claim about human safety.
 (C)  This strongly weakens rather than supports the claim, as it shows the same sweetener caused cancer in 53 of 500 mice, suggesting it might be carcinogenic after all.
 (D)  This weakens the claim by showing that rat studies can sometimes fail to identify chemicals that are carcinogenic in humans, undermining the reliability of the rat study.
 (E)  This weakens the claim by suggesting the experiment may have been terminated prematurely, before more cancers had time to develop. If the rats' average lifespan is 2 years but they were only studied for 13 months, many potential cancer cases might have been missed.

KarishmaB · Answer

I am unable to follow your logic here. The company stopped observing 7 months before the rats died. This weakens their conclusion. They should have observed the rats up to 2 years - the age of their natural death. If they did not get cancer throughout their life, then the sweetener can be said to be safe. What if in those 7 months many rats developed cancer? Then it seems that the sweetener could be carcinogenic.

A chemical company claims that, since only one of 520 rats that were

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A chemical company claims that, since only one of 520 rats that were

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