This past holiday weekend, the number of traffic accidents that occurr

(A) Traffic accident rates on the particular stretch of Highway 79 will continue to drop as long as the Highway Patrol’s publicity campaign continues.
- This need not be assumed for the conclusion to be valid.

(B) The two holiday weekends cover exactly the same calendar dates.
- "...number of accidents last year in the same location over the same holiday weekend"- this is already mentioned in the passage.

(C) Highway Patrol cars are patrolling the particular stretch of Highway 79 more frequently.
- Publicity campaign need not necessarily be patrolling only.

(D) The total number of miles driven on the particular stretch of Highway 79 has not decreased 25% or more since last year.
- CORRECT. If the number of miles have decreased by 25% or more, then the conclusion cannot be inferred.

(E) A reduction in speeding is the only driving habit that has improved since last year.
-Irrelevant.

Answer D.

Yes, these are also good driving habits, and the campaign may have improved these habits as well (we can't say for sure). And that is exactly why option (E) is incorrect: "reduction in speeding is the only driving habit" need not be assumed for the conclusion to be valid.

Can you please explain why E is incorrect? And also, how can we surely state '25%' in option D?

Can anyone explain why E is incorrect? My understanding is that in an assumption question, we need to look for a necessary condition, such that if the statement is negated, my argument would fall. The argument is that Highway Patrol's publicity campaign against speeding has resulted in safer driving habits amongst motorists. While I do understand D, isn't E correct too? If I were to negate E and say that the reduction in accidents happened due to some other reason, like cases of drunken driven fell in the last one year, wouldn't it prove that E is correct too?

An assumption is a statement that must be true for the conclusion to hold.
Apply the NEGATION TEST.
When the correct answer is negated, the conclusion will be invalidated.

Conclusion:
The Highway Patrol’s publicity campaign against speeding has resulted in SAFER DRIVING HABITS.

E, negated:
A reduction in speeding is not the only driving habit that has improved.
In other words:
OTHER DRIVING HABITS -- aside from a reduction in speeding -- have improved,.
This negation STRENGTHENS the conclusion that the campaign has resulted in safer driving habits.
Since the negation of the correct answer must invalidate the conclusion, eliminate E.

D, negated:
The total number of miles driven on the particular stretch of Highway 79 has decreased 25% or more since last year.
Here, the 25% reduction in the number of accidents can be attributed to the 25% reduction in the number of miles driven, WEAKENING the conclusion that the campaign against speeding resulted in safer driving habits.
Since the negation of D invalidates the conclusion, D is an ASSUMPTION: a statement that MUST BE TRUE for the conclusion to hold.

This past holiday weekend, the number of traffic accidents that occurred on a particular stretch of Highway 79 was 25 percent lower than the corresponding number of accidents last year in the same location over the same holiday weekend. This is good evidence that the Highway Patrol’s publicity campaign against speeding has resulted in safer driving habits among motorists.

Which of the following is assumed in reaching the conclusion above?

(A) Traffic accident rates on the particular stretch of Highway 79 will continue to drop as long as the Highway Patrol’s publicity campaign continues. - WRONG. Talks about future instead of the moment that passage deals in.

(B) The two holiday weekends cover exactly the same calendar dates. - WRONG. Not necessarily true. Even if so, it does not impacts the campaigning claim that passage makes.

(C) Highway Patrol cars are patrolling the particular stretch of Highway 79 more frequently. - WRONG. Needs further assumption that would support it to stand a chance of being the answer. And if it is not so the case then too it has no impact in the passage.

(D) The total number of miles driven on the particular stretch of Highway 79 has not decreased 25% or more since last year. - CORRECT. Had it decreased then the claim of the passage loses out that campaign had impact on the driving habits. 

(E) A reduction in speeding is the only driving habit that has improved since last year. - WRONG. Not a necessary requirement. Also, if it is not true then it would indirectly say that other habits improved thus supporting the conclusion.

Answer D.

chetan2u sir, in conclusion it is mentioned that the campaign has reduced the speeding as it was against speeeding - hence I chose option E as it says that the speeding has reduced & basis that assumption the accidents have gone down. Speeding came down. It was not nothing else, just speeding i.e. no reduction in the no. of vehicles, no reduction in the length of the highway, but very specifically speeding that reduced...Can you pls point out where am I wrong in my assessment.­ How can we assume that reduction in the accidents is necessarily correlated to the length of the highway? I understand D & why it is correct, not why is E wrong.

 

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Two reasons:-

1) E is too extreme: It uses the word only, but say speeding has improved and so has use of seat belts. Does it tell us that speeding would not be a reason for bringing down accidents.
2) Conclusion: Conclusion is not about speeding but about the speeding programme that has inculcated good driving habits. The conclusion itself mentions that campaign against speeding has resulted in safer driving habits among motorists, while the assumptions limits the habits to just speeding.

On the other hand, E says that 25% accidents going down are true numerically, that is accident per mile driven is low. For example, say last year 100,000 miles were driven with 100 accidents so 1 accident per 1000 miles driven, whereas this year only 10,000 miles were driven and there were 70 accidents, that is 7 accidents per 1000 miles. This shows the number of accidents have gone down but the intensity per mile is much more.