Although only 2 percent of drivers on Lalalands highways drove sports

Question

Although only 2 percent of drivers on Lalaland’s highways drove sports cars, 25 percent of all vehicles ticketed for drunk driving in the past 90 days were sports cars. Clearly, sports car drivers on Lalaland highways are more likely to drive drunk than are drivers of other kinds of vehicles.

The conclusion drawn above depends on which of the following assumptions?

(A) Drivers on Lalaland highways drive drunk more often than do drivers on highways not covered in the report.

(B) Many of the vehicles ticketed for drunk driving were ticketed more than once during the time period covered by the report.

(C) Drivers who are ticketed for drunk driving are more likely to drive drunk regularly than are drivers who are not ticketed.

(D) The number of drivers ticketed for drunk driving was greater than the number of sportscars.

(E) Drivers of sports cars are less likely to be ticketed for drunk driving than are drivers of other kinds of cars.

pqhai · Accepted Answer

This question uses a very classic logic assumption –  Statistical Assumption . It is similar to hypothesis you see in Probability & Statistics of Quantitative.

The form is: 
 A is more likely to do X than B is
Assumption: Over the statical period, A does X  more often  than B does.

For example: 
Team A has more chances to win this game than Team B does.
Assumption: Over the statical period, Team A wins  more often  than Team B

More example: 
Mount A is more likely to have volcano than Mount B is
Assumption: Over the statical period, Mount A has volcano  more often  than Mount B

APPLY TO THIS QUESTION:

Fact: only 2 percent of drivers on Lalaland’s highways drove sports cars, 
Fact: 25 percent of all vehicles ticketed for drunk driving in the past 90 days were sports cars. 
Conclusion: Sports car drivers on Lalaland highways are more likely to drive drunk than are drivers of other kinds of vehicles.
  Assumption:   Over the statical period, sport car drivers drives drunk  more often (more regularly)  than drivers of other kind of vehicles do.

ANALYZE EACH ANSWER:

A)Drivers on Lalaland highways drive drunk more often than do drivers on highways not covered in the report. 
 Wrong.  Out of scope. Nothing about “drivers on highways not covered…”. We just talk about Lalaland highways.

B)Many of the vehicles ticketed for drunk driving were ticketed more than once during the time period covered by the report.
 Wrong.   TEMPTING.  Why? The wording is quite simple, but if you do not read carefull, you may assume “many of the vehicles ticked for drunk driving more than once” are “sport vehicles”. However, B is wrong because  B does not say these vehicles are sport cars . If that was the case, B would be correct assumption. But what if the vehicles ticked for drunk more than once may NOT be sport cars.
 
C)Drivers who are ticketed for drunk driving are more likely to drive drunk regularly than are drivers who are not ticketed. 
  Correct.   This is exactly assumption stated above.

D)The number of drivers ticketed for drunk driving was greater than the number of sportscars. 
 Wrong.  We do not compare the number of drivers vs the number of sportcars.

E)Drivers of sports cars are less likely to be ticketed for drunk driving than are drivers of other kinds of cars.
 Wrong.  It’s a reverse answer. Hence, E is wrong.

Hope it helps.

pqhai · Answer

Hi mneeti

First of all, B and C are totally different in meaning. Let analyze.

B)Many of the vehicles ticketed for drunk driving were ticketed more than once during the time period covered by the report. 
B is wrong because B only mentions that those who were ticketed for drunk driving will be ticketed again during the time period. But  what if those who were ticketed more than one time are are drivers of other kinds of vehicles, NOT drivers of sport vehicles.  If that’s the case, you cannot conclude drivers of sport vehicles drunk more regularly than drivers of other kind of vehicles do.
Hence, B is not the assumption.
 
 C)Drivers who are ticketed for drunk driving are more likely to drive drunk regularly than are drivers who are not ticketed. 
C means those who are ticketed fro drunk driving are more likely ticketed again.  It does not matter drivers of sport cars or other kind of cars.   This is the base for a comparison between the number of ticket/driver of sport cars AND the number of ticket/driver of other kind of cars.

Name “drivers of sport cars” is SET 1, name “drivers of other kind of cars is SET 2. 
So,  if the number of ticket/driver of SET 1 is greater than that of SET 2, the conclusion is correct.

Let analyze an example:

Assume we have 1000 drivers
SET 1 accounts for 2% = 20 drivers
SET 2 accounts for 98% = 980 drivers

Assume we have 100 tickets for drunk driving.
SET 1 accounts for 25% = 25 tickets
SET 2 accounts for 75% = 75 tickets.

Ticket / Driver: 
20 drivers of sports cars got 25 tickets ==> 1.25 ticket / driver
980 drivers of other kind of cars got 75 tickets ==> 0.07 ticket / driver
Clearly, drivers of sport cars are more likely are more likely to drive drunk regularly than are drivers. Hence, C is the assumption.

Hope it helps.

BeckyRobinsonTPR · Answer

this assumption question relies on the connection between 25 % and more likely. Assuming that if a higher percentage of people have something happen to them then that makes it more likely. The answer choices are designed to distract the reader with other, irrelevant issues.

mneeti · Answer

Hi, could you please elaborate a little more. I am not able to catch the exact point in 'C'.
The explanation you haven for negating 'B' applies to 'C' as well as in even 'C' doesn't talk about the sports cars. So, I am unable to figure out why 'C' is a better option than 'B'.

thuygiang7 · Answer

Hi all,

Could you kindly share: when i negate the answer C, the conclusion does not break:

"Drivers who are ticketed for drunk driving are more likely to drive drunk regularly than are drivers who are not ticketed."
--> Negation: "Drivers who are ticketed for drunk driving are not more likely to drive drunk regularly than are driver who are not ticketed."

Even with this negation, the conclusion still holds "sports car drivers on Lalaland highways are more likely to drive drunk than are drivers of other kinds of vehicles", because "2 percent of drivers on Lalaland’s highways drove sports cars, 25 percent of all vehicles ticketed for drunk driving in the past 90 days were sports cars".

Could someone help to clarify?

Many thanks

RiyaJ0032 · Answer

but in your argument, the 980 drivers who got 75 tickets (0.07 ticket/driver) make up the group who drive drunk but who do not own a sport car

so essentially the assumption as per your reasoning is that, drivers who drive drunk and are ticketed but do not own a sport car are less likely to drive drunk than drivers of sports car who drive drunk and are ticketed

whereas (c) does the comparison b/w drivers who are not ticketed (means non drinkers) and ticketed drivers who are sports car owner (drinkers)

can someone please explain this?

MartyMurray 
 IanStewart 
 DmitryFarber 
 KarishmaB

IanStewart · Answer

I don't really post here any more, but I felt I needed to comment on the absurdity of this question -- nowhere in America is it true that drivers get "ticketed" for drunk driving and just drive off. People go to jail for that.

I skimmed the replies in this thread, including the one you quoted, and I don't think any of them capture the logic here correctly. The argument in the stem involves a straightforward scope shift, one you should learn to recognize instantly because these kinds of scope shifts crop up all the time in CR (and in potentially faulty arguments in the real world). The evidence in the stem is about  tickets  for drunk driving. The evidence perfectly supports the conclusion that sports car drivers get more *tickets* for drunk driving. But that is not the conclusion -- the conclusion is that sports car drivers are actually doing more drunk driving. The argument is assuming that the people getting more tickets are the people who are driving drunk more often. That might very well be true, but it is not something we  know  to be true -- perhaps the police don't like sports car drivers much and pull them over far more often than other drivers, or perhaps the police only look for drunk drivers in certain neighbourhoods which are home to a ton of the sports car drivers. The argument only works if it assumes that, by looking at tickets alone, you get reliable evidence about rates of drunk driving. Otherwise the evidence is not connected to the conclusion.

You'll encounter arguments like this all the time in the real world also -- for example, politicians will often say "fewer people were arrested this year, therefore the crime rate went down." That might be true, but those politicians are making a possibly-incorrect assumption that the arrest rate gives a reliable indication of the crime rate.

Although only 2 percent of drivers on Lalalands highways drove sports

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Although only 2 percent of drivers on Lalalands highways drove sports

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