Bats Laboratory

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perfectstranger: Master | Next Rank: 500 Posts; Posts: 177; Joined: Wed Jul 16, 2008 11:06 amFollowed by: 1 member; Thanked: 2 times

by perfectstranger » Sun Jul 20, 2008 1:16 am

A certain laboratory is studying the incidence of fatal liver damage in rats.-Sixty-five percent of all rats whose environments exposed them to low levels of the toxin sulfur dioxide died of liver disorder. Ninety percent of all rats who died of liver disorder, however, were not exposed to any environmental toxins.

Which of the following would provide a feasible explanation for the statistics above?

A Environmental and nonenvironmental causes of liver disease in rats are mutually exclusive.
B There is only one cause of fatal liver disease in rats.
C Environmental toxins are not particularly dangerous to the livers of rats.
D Only a small portion of the entire group of rats studied was exposed to environmental sulfur dioxide.
E Most rats will not suffer from exposure to low levels of sulfur dioxide.

Please explain the answer in a detailed way.

Source: Beat The GMAT — Critical Reasoning | Sun Jul 20, 2008 1:16 am

raunekk: Legendary Member; Posts: 1159; Joined: Wed Apr 16, 2008 10:35 pm; Thanked: 56 times

by raunekk » Sun Jul 20, 2008 3:26 am

IMO:D

LET Total number died due to liver damage =1000

Total no. of rats whose environments
exposed themselves to low levels of
the toxin sulfur dioxide (& under
observation) =100

65% of them died = 65

Therefore,rats who died of liver disorder,
who were not exposed to any environmental = 900 (1000-100)
toxins
(i.e 90%)

Thus % of rats exposed to sulfur dioxide = 10% ( 100 of 1000)

Which obviously is a small portion (of 1000 )
under observation for toxin.

D says exactly this.

Thx.

NSNguyen: Master | Next Rank: 500 Posts; Posts: 401; Joined: Fri May 04, 2007 9:21 amFollowed by: 1 member; Thanked: 3 times

by NSNguyen » Fri Jul 25, 2008 6:49 am

10% total rats died of disorder are exposed to low level of sulfur dioxide
90% rats died of liver disorder are not exposed to ....

OA: D

Please share your idea and your reasoning

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DiverJ: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Feb 10, 2009 11:14 am

by DiverJ » Fri Feb 13, 2009 10:55 pm

I came across this question as well and the responses here don't seem logical to me. Why are you assuming that the total # of rats that died is 1000 and that the sample of exposed rats was 100. If you flip those numbers around then you'd get the opposite answer.

What if 1000 rats were exposed and 10 were not exposed. Then 650 died of liver disorder after exposure and 9 died of liver disorder without exposure.

The two stats come from different sample groups. 1) Rats exposed 2) Rats not exposed.

I don't see how you'd be able to tell that the population sizes were different.

Does anyone else have an answer to this one?

bmlaud: Master | Next Rank: 500 Posts; Posts: 174; Joined: Thu Jan 08, 2009 12:04 am; Thanked: 5 times; GMAT Score:620

by bmlaud » Sat Feb 14, 2009 1:30 am

Let the total no. of rats died of liver damage be 1000
then no. of rats died without any effect of env. toxins = 90% of 1000 = 900
No. of rats died due to sulfur di oxide = 100 .... (1000-900)

No. of rats exposed to sulfur di oxide = 100/0.65 = 154

154 <<< 900 ( which is the no. of rat deaths for other reasons), the sample size will atleast be 900.

so D

graem83d: Master | Next Rank: 500 Posts; Posts: 108; Joined: Tue Aug 05, 2014 3:00 am

by graem83d » Sun May 15, 2016 2:39 am

I would go with option D as the correct option

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