Critical Reasoning: Weaken the Argument

[calvincolton]

For the last five years, the XYZ Courier Company has made regular delivery trips between Town A and Town B. The average time taken by the company’s drivers to drive the round trip between the two towns, excluding the time taken for loading, unloading, and delivery, over that period has been 80 minutes. John, a driver for XYZ, needs to make a personal trip between the two towns; he figures that he should allow approximately 80 minutes for the round trip.

Which of the following, if true, does not call John’s conclusion into question?

a) The route between Town A and Town B has been plagued by increasing congestion over the last five years, as the area's population has doubled during that time.

b) Most of XYZ’s courier vehicles are heavy trucks, for which speed limits are lower than for passenger vehicles.

c) Many of the packages carried by XYZ between Town A and Town B are large, high-security packages, for which the processes of loading, unloading, and delivery can take up to half the length of the trip itself.

d) John will make his personal trip at an hour when XYZ does not make delivery trips.

e) Before a freeway was built between Town A and Town B two years ago, the only routes between the two towns were state highways with multiple traffic lights and reduced-speed downtown zones.

The correct answer, as stated by Manhattan is C, the explanation as follows:
John assumes that his round-trip driving time between the two towns will be similar to XYZ’s average time, over the last five years, for the same round trip. Therefore, John’s conclusion will be weakened by (a) any systematic difference between John’s personal trip and XYZ’s company trips, or (b) any reason why the five-year average is not representative of the time currently required to drive between the two towns.

b) The cited round-trip time specifically excludes the time required for loading, unloading, and delivery, so the length of time taken by these tasks is irrelevant to the conclusion at hand.

I chose answer choice E under the premise that John's conclusion be strengthened, and thus not called into question, by a higher five-year average not representative of the current and possibly shorter time required?

If the average time of a round-trip for the first three years was 100 minutes and 50 minutes for the last two years (still an average of 80 minutes), then John's conclusion should not be questioned--50 minutes of driving the round trip and additional time for his personal trip. Implying that the lack of a freeway increased travel time for the first three years should lead to this conclusion and thus strengthen John's conclusion.

Please clarify.

[arnabgangully]

Actually what ever time it takes for loading or unloading the packages for the courier company XYZ,it already provided that it is ignored and the remaining time for the travelling only is 80 min.If this information was absent then this option would have been the correct one.

[jnelson0612]

Aha! Actually, this question is a "Weaken Except" question--all the answer choices will weaken the conclusion EXCEPT one.

Usually in this scenario the right answer (the "except") will not be the opposite but rather something that is irrelevant. In this situation, it is natural to look for something that strengthens, but the correct answer is more likely to be something completely irrelevant to the argument.

Take a look at this thread for more discussion of the answer choices: cr-special-delivery-t13700.html