Assumption CR

abhi75 · Posted: Sat Apr 12, 2008 2:28 pm Post subject: Assumption CR

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.

Can someone please explain the concept behind this one and how to attach such kinds of questions.

Thanks in advance.

simplyjat · Posted: Sat Apr 12, 2008 2:46 pm Post subject:

In my opinion the answer is D

The problem with argument is comparison of combined percentages with individual percentages.
Lets take some number to illustrate further...

Total number of victims = 100
Total number of drivers amongst victims = 70
Total number of front seat passenger amongst victims = 30
Total number of drivers not wearing seat belts = 68
Total number of front passengers not wearing seat belts = 12

now the correlation between seat belt and driver is strong 68/70, but the correlation between seat belt and front passengers is 12/30. This means that it might be helpful for drivers to wear seat belt but there might be no advantage for front passengers....

abhi75 · Posted: Sat Apr 12, 2008 3:42 pm Post subject:

Thanks for the reply simplyjat.

I picked D too however thats not the OA. Therefore I am trying to relate this to the OA.

OA is A.

Say the number of accidents in Dole state = 100
Passengers and drivers severely injured = 90 (assume)
From the information given 80% of severely injured do not wear seatbeat which is 72. The rest 18 will be wearing seatbelt.

So the total wearing seatbelt = 18 + 10 = 28

Whichever numbers you pick the drivers wearing seatbelt will always be more than 20.

and therefore the OA is A.

But again, this seems like a deduction rather than an assumption. In the real exam I would just pick D and move ahead.

Can other resident expert shed some light on this kinds of problem.

Stuart Kovinsky · Posted: Sat Apr 12, 2008 5:04 pm Post subject:

An assumption is something that must be true for the argument to make sense.

Here, the author concludes that seatbelts greatly reduce the risk of front seaters getting severely injured, based on a survey that showed that 80% of people severely injured weren't wearing seatbelts.

What we don't know, however, is what % of people who were NOT seriously injured weren't wearing seatbelts.

For example, if it were true that 80% of people who were NOT severely injured weren't wearing seatblets, then seatbelts would seem to be irrelevant.

So, in order for the conclusion to be true, the author has to be assuming that less that 80% of those not severely injured were not wearing seatbelts.. or to turn that into a positive statement, that more than 20% of those not seriously injured WERE wearing their seatbelts.

Since 20% of the seriously injured weren't wearing belts, for the non-seriously injured to be above 20%, the total number of people wearing seatbelts must also be over 20%. Therefore, (a) MUST be true.

abhi75 · Posted: Sat Apr 12, 2008 5:43 pm Post subject:

Thanks Stuart for a great explanation.