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percent and ratio

by tanviet » Sun Mar 08, 2009 4:21 am
pls, help with this question. this question is from 1000RC pack and so an official one (question 14 test 2)

14. A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.
The conclusion above is not properly drawn unless which of the following is true?
(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents.
(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.
(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.

OA is A but I do not understand, pls, help
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by srn » Sun Mar 08, 2009 4:57 am
The conclusion is - 'wearing seat belts can reduce the risk of being severly injured'.
The premise says that '80 percent were not wearing seat belts at the time of their accidents'.

The question actually asks what must be the assumption so that the conclusion be true.
Clearly, it should be that the remaining 20% in the survey must have been wearing seatbelts. Hence A is correct.

B is wrong as it is irrelevant to the survey.
C,D,E are wrong as it no way addresses the conclusion.
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by tanviet » Sun Mar 08, 2009 7:03 pm
no, "80 % of the severely injured persons" not " of persons in the study"

how A can be an asssumption
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by karmayogi » Sun Mar 08, 2009 9:17 pm
duongthang wrote:no, "80 % of the severely injured persons" not " of persons in the study"

how A can be an asssumption
I am in accord with you. I also don't feel A can be an assumption.
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by srn » Mon Mar 09, 2009 12:12 am
k..I overlooked it.

But I tried looking at it in a different way

Consider 100 ppl were considered for the survey of which say 50 ppl were severely injured. 80% of 50 ie 40 ppl did not wear seat bealts.
(i.e 20% ppl still wore seat belts and got severely injured)

Now the conclusion says that 'by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured'

For the conclusion to be true,

The remaining number of ppl in the survey who wore seat belts and did not get injured must be more than the 20% i.e the majority of them who wore seatbelts should not have got seriously injured

In other words, even if 20 % wore seat belts and got severely injured, we can say that wearing seat belts reduces the risk of being severely injured only if the remaining ppl in the survey is more than these 20% ppl who wore seat belts and got severely injured.

This means that more than 20% were wearing seatbelts. Hence A.
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by karmayogi » Mon Mar 09, 2009 1:24 am
srn wrote:k..I overlooked it.

But I tried looking at it in a different way

Consider 100 ppl were considered for the survey of which say 50 ppl were severely injured. 80% of 50 ie 40 ppl did not wear seat bealts.
(i.e 20% ppl still wore seat belts and got severely injured)

Now the conclusion says that 'by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured'

For the conclusion to be true,

The remaining number of ppl in the survey who wore seat belts and did not get injured must be more than the 20% i.e the majority of them who wore seatbelts should not have got seriously injured

In other words, even if 20 % wore seat belts and got severely injured, we can say that wearing seat belts reduces the risk of being severely injured only if the remaining ppl in the survey is more than these 20% ppl who wore seat belts and got severely injured.

This means that more than 20% were wearing seatbelts. Hence A.
Yet not convinced. Suppose there were 1000 people met with accident. 100 got seriously injured; out of these 100, 20 wore seat belt. Now as you pointed out, “The remaining number of ppl in the survey who wore seat belts and did not get injured must be more than the 20%,” the number of people who wore seat belt and not seriously injured must be greater than 20. Hence, the total number of people who wore seat belt must be greater than 40. Let’s assume 45, but 45 is not 20% of 1000.

Am I missing something?
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by delhiboy1979 » Tue Mar 10, 2009 1:16 am
i agree with Karmayogi there, infact I cannot see any of the options within scope. what is the source of this question?
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by S0laris » Wed Mar 11, 2009 1:59 am
... Suppose there were 1000 people met with accident. 100 got seriously injured; out of these 100, 20 wore seat belt. Now as you pointed out, “The remaining number of ppl in the survey who wore seat belts and did not get injured must be more than the 20%,” the number of people who wore seat belt and not seriously injured must be greater than 20. Hence, the total number of people who wore seat belt must be greater than 40. Let’s assume 45, but 45 is not 20% of 1000.

Am I missing something?

Yes U did. U mixed up the data tested in survey. There is nothing about pople who were injured not severely. The only questionalble assumption is whether those rest 20%, of all severely injured, were wearing sit-belts or not. If they were, as A choice shows, then the survey makes sence.
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by Ian Stewart » Fri Mar 13, 2009 9:48 am
The question tells us that 80% of injured drivers weren't wearing seat belts, and goes on to conclude that seat belts improve safety. Well, what if 80% of all drivers don't wear seat belts? Then the conclusion doesn't follow - seat belts don't make a difference, since you're equally likely to be injured regardless of whether you wear a seat belt. We certainly need some information about how many people actually wear seat belts, which is what answer choice A is getting at.
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by nicolette » Sun May 15, 2016 11:29 am
I would go with option A as the correct option
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