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.

The answer is A.
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Can someone plug in the numbers and explain this to me ...This is what an expert in other forum explained:
"Plug in that 100 in the survey were seriously injured.
According to the argument, 20 wore seat belts, 80 did not.
Negated, answer choice A would say that perhaps only 10% of all the drivers/passengers wore seat belts.
Since 20 = 10% of 200, we could have 200 total in the survey, 20 who wore seat belts, 200-20=180 who did not.
Since 80 did not wear seat belts and were seriously injured, and 180 in total did not wear seat belts, 180-80 = 100 did not wear seat belts and avoided serious injury.
Thus, a majority of those who did not wear seat belts would have avoided serious injury, invalidating the conclusion that seat beats prevent serious injury.
Since the scenario above invalidates the conclusion and is possible when answer choice A is negated, the argument is assuming that answer choice A is true: that more than 20% of the people in the survey wore seat belts."

Now my question is ..how can he equate 10% of X = 20, bcoz according to the arguement;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... i believe its 80% of seriously injured or should i remove the sentence between the comma and read 80% of all the auto accidents- i doubt this...

thanks for your help

A for me.

80% of SEVERLY injured were not wearing seat belts. This means 20 % of Severly injured were wearing seat belts. In addition, some of the non-severly injured would also be wearing seat belts. That means more than 20 % of all people were wearing seat belts if the conclusion has to hold true.

Crick