Burglar alarm systems can be inaccurate in two ways: they

Yes it's E and your method is faster than my method. Beautiful and simple.

This is the question where the assumption and the strengthen option, both are the same.

If the question would have been that what can be assumed for the argument to be true, then also the option E would have been the correct answer.

WTF ? .................................

A has a direct connect to the argument as it would result in a waste of resources

This Portion is Premise for sure:
Premise: Burglar alarm systems can be inaccurate in two ways: they can fail to detect an intruder when one is present, or they can falsely report the presence of an intruder.

This is argument or Premise-
To detect the presence of an intruder most accurately, homeowners should purchase the system that is least likely to falsely report the presence of an intruder.

The answer is obviously E. Here, what is the gap? The conclusion overlooks the first way, though he points out the two. Strengthening question needs to bring a new piece of evidence that can save the author from the logical gap. The option E rules out the first way stating that no benefit on streesing on the first way. Rather, do something with the second way.
Option A is after a intruder detected.so, Offtopic.
B is actually weakening the point, since if so, the recommendation is worthless to purchase special one.
C Offtopic.
D better than other wrong answers but still, not clearly ruling out the first way, wich option E does beautifully.

So option A fixes the gap or introduces the necessary assumption to support the conclusion.
If option E is negated, then conclusion will fail.

Burglar alarm systems can be inaccurate in two ways:

I. they can fail to detect an intruder when one is present,
or
II. they can falsely report the presence of an intruder.

To detect the presence of an intruder most accurately, homeowners should purchase the system that is least likely to falsely report the presence of an intruder.(ie., conclusion says that system which fails less in case II is preferred.)

If true, which of the following would most strengthen the above recommendation?

A) The police respond to automatic alerts from burglar alarms more quickly than they do to telephone calls reporting the presence of an intruder.............we are bothered which alarm to select not whether alarm or phone call. OFS

B) The burglar alarm system that is least likely to sound its alarm when there is no intruder present is equal in price to all other major brands of alarm systems..........price is not of concern here. OFS

C) Local police forces vary in their response rates to burglar alarm systems..............how police systems work is not needed here. OFS

D) All burglar alarm systems have the same rate of mistaking an animal for a burglar..............animal plays the spoilsport here. OFS

E) All burglar alarm systems have the same rate of failing to detect an intruder when one is present...............this indicates that ou tof the two cases above case I need not considered since it is same for all systems. This strengthen the conclusion saying that remaining case II is important here.

Quite an easy E for me

I treat it as an assumption question

Given:
Two reasons for inaccuracy in alarms-
1) fail to detect an intruder when one is present.
2) falsely report the presence of an intruder.

Conclusion:
To be more accurate- purchase the system that is least likely to falsely report the presence of an intruder.
i.e. the conclusion is based only on 'reason 2' above. It asks homeowners to minimize reason 2 and in-turn increase accuracy.

But what about reason 1?? If minimizing reason 2 alone increases the accuracy, the reason 1 should either be constant or be going down by itself among all available alarms out there(ignore the second part).

Option E says precisely this.

I spent 1:12 doing this question. I got it correct, but in truth I was kind of cowboy-ing it to show off a little. It would probably take me a solid 1:30, perhaps even 1:45 on the actual day.

First things first people, you have to keep an eye out for the obvious wrong answers. Make this a game of probability.

This line should jump out at you To detect the presence of an intruder most accurately to knock off a few freebies.


A) The police respond to automatic alerts from burglar alarms more quickly than they do to telephone calls reporting the presence of an intruder.

This is simply irrelevant. Focus on the issue, people! We're trying to find out which way is most accurate to detect an intruder. Not whether the police are going to respond to an alarm. This answer choice trips those who don't keep their eye on the ball. Grrr.

B) The burglar alarm system that is least likely to sound its alarm when there is no intruder present is equal in price to all other major brands of alarm systems.

Again, this should be a straight elimination. What's price got to do with the ability to detect? What does it matter that an alarm that is least likely to sound its alarm is comparable in price to other major brands of alarm systems? I didn't even read this entirely before eliminating it, I think.

C) Local police forces vary in their response rates to burglar alarm systems.

C is just a worse version of B. This is a freebie elimination.

D) All burglar alarm systems have the same rate of mistaking an animal for a burglar.

This is a close but no cigar answer choice. It brings into the conversation something about rates. Of course, the fact it brings up animals is a red flag, so, to be conservative I'd keep it, but move on for something better.

E) All burglar alarm systems have the same rate of failing to detect an intruder when one is present.

Bingo. And we're done. If all the alarms have the same rate of failing to detect when one is present --- then getting the best system that is least likely to falsely report the presence of an intruder is the optimum route to take.

I'm wondering how true all this stuff about police response is now!

I would like a better explanation for this question

First thing I'll say is that I have some minor qualms about some of the verbiage in this question, but I'll tell you my process as I did the problem:

I'll give it a go and will describe how I thought through the problem.

First I read the question.



This is a 'strengthen the argument' question, so I will be dealing with 'premise/conclusion/assumptions.'

I go to the argument to deconstruct.



Okay so first I ID where the conclusion is. The conclusion is the second sentence.

CONCLUSION: a system that is least likely falsely report an intruder will detect the presence of intruders most accurately.

The premise is a little wonky, but it's basically: "Two ways to be inaccurate: NOT detecting an intruder that IS there; or DETECTING an intruder when there ISN'T one."

Now here's where my GMAT experience kicked in (though I think I have some qualms with the language used).

It's easy to read the conclusion as ONLY about the systems ability to ID an intruder that is there. BUT, my GMAT spidey-sense told me that the conclusion was about the OVERALL accuracy.

That is: "To detect the presence of an intruder most accurately" is meant to mean 'detecting presence when there is an intruder and also NOT detecting an intruder when there isn't."

But, I... take some umbrage with this. I think the conclusion should be written "To ensure a system that is most accurate," or "To ensure that a system makes as few mistakes as possible."

The language used seems too focused on avoiding ONE of the two errors (missing an intruder when there is one), when the question is actually about avoiding BOTH errors.

So... chalk that up to my GMAT spidey sense.

Given that I figured this is what the conclusion was really going for, and given that the passage thinks that 'a system that doesn't falsely report an intruder will be most accurate,' I figured that what would need to be true is that all systems are equally good at detecting an intruder when there is one. Answer E stated exactly that.

It's a somewhat annoying question because of this verbiage. I'm not sure it's an official question or not, but usually official questions would be more careful and precise.

EDIT:

You could think of the conclusion as "This system will detect presence of a burglar most accurately" and the premise as "Purchase a system that is least likely to falsely report the presence of an intruder."

I think to some degree I 'felt' that this was the argument, and part of the reason my spidey sense kicked in was that this logic makes the most sense if the conclusion is about OVERALL accuracy, not just 'accurately detecting a burglar when there is one.' One of the questions I asked myself was "Do systems that do not falsely report an intruder also not MISS an intruder when there is one?" I supposed this could be the case, but it really seemed to me like the the problem was emphasizing that the two 'failures' were distinct, so I was also wondering how the conclusion could be true if a system's 'accuracy' for the two kinds of errors was NOT linked. If that were the case, the conclusion only makes sense if it is about OVERALL accuracy.