Traverton s city council wants to minimize the city s

Comparison for Cost effecting solution is between incandescent bulbs and LED's. You got carried away by the statement "Whether Traverton’s city council plans to increase the number of traffic signal lights in Traverton"

Even if it plans to increase the number still the comparison will be between incandescent bulbs and LED's.

X number of LED are cost effective than X number of incandescent bulbs

Even if the city plans to increase the traffic lights say by a Factor of Y

Still X+ Y number of LED will be cost effective to X+Y number of incandescent bulbs. Does this all make sense to you?

Thus, D doesn't help us to reach anywhere.

adkikani,

As stated by ani007garg, we are asked, "Which of the following would it be most useful to know in determining whether switching to LED arrays would be likely to help minimize Traverton’s yearly maintenance costs?" Imagine that Traverton currently has 100 traffic signal lights and each of those lights costs $50 per year (ie cost of electricity) using incandescent bulbs (so $5,000 total in energy costs). Switching to LEDs might reduce the annual energy cost per light bulb to $40, bringing the total annual energy costs down to $4,000.

Now, what if, as suggested in choice D, Traverton increases the number of traffic signal lights from, say, 100 to 200? If they stick with incandescent bulbs, the total annual energy cost will be $10,000, but if they change to LEDs, the total annual energy cost will be $8,000. Yes, it is true that $8,000 is more than the original annual cost using incandescent bulbs ($5,000), but $8,000 is cheaper than $10,000; therefore, based on annual energy costs, switching to LEDs would indeed help minimize Traverton's yearly maintenance costs, regardless of how many bulbs they have (or plan to have in the future). Now, if those LEDs only last half as long as the incandescent bulbs, that means Traverton will have to spend more money replacing bulbs if they convert to LEDs. This additional cost might offset the energy cost savings, in which case switching to LEDs might not help minimize Traverton's yearly maintenance costs.
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Option A..... else reason "LED arrays consume significantly less energy and cost no more to purchase." would be nullified since LEDs would be bought and exchanged more freq than the incandescent bulbs!

another sub-400 level question. A is blatant

I got this wrong.

In option A) Whether the expected service life of LED arrays is at least as long as that
of the currently used incandescent bulbs.

The para states that LEDs consume significantly less energy and cost the same.

For example

Energy savings per year caused by the change from incandescent to LED = 1000000$
But LEDs last for 52 weeks, while incandescent last for 53 weeks.
The answer to the question, "Whether the expected service life of LED arrays is at least as long as that
of the currently used incandescent bulbs" is no here. But it would still make sense to shift from incandescent to LED, because the difference is less.

It significantly reduces energy consumption, so the only reason to not change from incandescent to LEDs would be if the service life of LEDs was significantly lesser than that of incandescent bulbs. It need not have a service life at least equal to that of incandescent.
It would be very important to know what the service lives of each of them are, so we can make a calculated decision. But the answer to the question - "Whether the expected service life of LED arrays is at least as long as that
of the currently used incandescent bulbs." tells us nothing.

Why is D wrong?
I was stuck between A & D

(A) Whether the expected service life of LED arrays is at least as long as that of the currently used incandescent bulbs
we are evaluating but for me D looks more strong enough
(D) Whether Traverton’s city council plans to increase the number of traffic signal lights in Traverton
council plans to increase the number, yearly costs wont minimize!

OG2017 CR553 P513

Traverton’s Traffic Lights
 
Step 1: Identify the Question

The phrase most helpful to know in determining in the question stem indicates that this is an Evaluate the Argument question.

Step 2: Deconstruct the Argument

Conc: replace bulbs with LEDs to << costs
b/c…
consume < energy
no more to purchase
not costly to change

The argument provides several cost advantages associated with switching to LEDs. Are there any other potential costs not discussed?

Step 3: Pause and State the Goal

On Evaluate questions, the goal is to find a piece of information that would be important to know to determine whether the conclusion is valid.

Step 4: Work from Wrong to Right

(A) CORRECT. The life of LEDs compared to current bulbs will affect how frequently they need to be changed and thus directly influence maintenance costs. If the life is about the same or LONGER, then switching may help to minimize costs. If the life is much SHORTER, however, then switching may cause costs to increase.
(B) The decisions by other towns to use LEDs do not affect the maintenance costs in Traverton.
(C) The source for purchasing incandescent bulbs versus LEDs does not directly affect costs.
(D) The number of traffic lights does not influence the relative costs of using LEDs versus incandescent bulbs. Each light source will still need a bulb.
(E) Whether the same crew can handle LED conversion does not have a direct impact on costs. Moreover, fixture conversion represents a onetime expenditure that will not influence ongoing maintenance costs.
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I chose D with below reasoning:
Although IB and LED arrays costs almost same, since energy consumed by LED arrays is less, this would help in minimizing T's yearly costs. If while increasing no of lights (as suggested in D), they use more LED arrays then my maintenance costs will be lower. What is incorrect with my reasoning?
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The question asks to minimise yearly average costs. It does not ask whether the cost will increase/decrease from previous year

Sent from my ONEPLUS A3003 using GMAT Club Forum mobile app

OA is A but I have a kind of disagreement with. As it is given in argument "as the incandescent bulbs burn out"(means LED wouldn't burn out or better service life) is given the answer to Option A so further determining same thing is not be the correct option. IMO answer should be E.

I think you might be misunderstanding this part of the passage: "as the incandescent bulbs burn out". This means that WHEN an incandescent bulb burns out, it will be replaced with an LED (as opposed to replacing all of the incandescent bulbs all at once, regardless of whether they are burnt out).

The use of "as" in this sentence is similar to the following sentence: "As guests arrive, the hostess will take their coats." Here "as" is used to describe when something is happening. In this case, "as" is NOT used as a comparison (i.e. (just) as). I believe you interpreted this phrase to mean: "SINCE the incandescent bulbs burn out...."

As for choice (E), we need to determine "whether switching to LED arrays would be likely to help minimize Traverton’s yearly maintenance costs". Even if we have to spend some money up front to retrain workers, this one-time up-front cost will not affect YEARLY maintenance costs in the long run. Besides, we are already told that the cost of converting the fixtures would be minimal. We also don't necessarily need the CURRENT crews to install the LEDs. Whether the bulbs are replaced by current crews or other crews, we need to know how the change will impact yearly maintenance costs. Choice (E) does not help.

And welcome to GMAT Club, vksharma!
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I do not agree with your reasoning for option D here. Option D says plans to increase. That means they have not increased the number of traffic signals yet.
If you think that the city would first increase the number of bulb signals and then change those new bulb signals with the LEDs, then I guess it is non sensical to first add bulbs to the new signals and then replace them with LEDs.

Point here is the argument talks about average yearly expenditure which will remain same for even if you increase the number of traffic signals.

Posted from my mobile device

But don't you think it is foolishness to first use the bulbs in new traffic signal lights and then replace them with the LEDs. My point is LEDs with be X +Y and Bulbs will be X. Now how will you compare them?

Hi GMATNinjaTwo, would you please confirm whether my reasoning is valid.

I thinks D is hard to assess, because D say increase the number of lights, but how many ? we don't know. the prompt does not tell us.
suppose, increase 100 lights, the yearly maintain cost almost same, while increase 101 , the yearly maintain cost increase significant.
then as long as the increases are fewer than 100, then two paths( increase 1 light and increase 100 lights), then both results are almost same, (no matter increase 1or 100, the yearly costs are almost same)
once the increases are more than 100, then the yearly costs are almost same.

Please confirm

Thanks in advance.
>_~

zoezhuyan, the passage does not say that Traverton wants to DECREASE the city’s average yearly expenditures on its traffic signal lights. Regardless of how many light bulbs Traverton has, adds, or plans to add, we want to MINIMIZE the cost. In other words, given any number of bulbs, will the city’s average yearly expenditures on its traffic signal lights be lower if they switch to LEDs?

That was the idea behind this post. Sure, the total annual costs increased from $5,000 to $8,000. But if we had NOT switched to LEDs, the costs would have risen from $5,000 to $10,000. So even though the costs have increased, we have still minimized those costs. The number of bulbs that the city needs is not relevant to this argument. Also, the total change in costs (up, down, or neither) compared to this year is not important. Whether they add a single bulb or a million bulbs, we want to know whether switching to LEDs will minimize the annual costs.

I hope that makes sense!
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Thanks so much GMATNinja,
Now i got it. at first, i mistook minimize with reduce.
excellent explanation.

Have a nice day
>_~

adkikani
Hello,
I hope you're doing good.

I just read this post of yours and thought: How angry it would have made you feel to get an easy question wrong back then Happens with me too sometimes.

I guess we all keep learning.

P.S: There is no intention to make this post useful. I just read your post and thought to post a comment

I agreed with this analysis and it brings up some great points, but rethinking this 1000 times over, and with the added benefit of hindsight, here is my analyzed thought process (in case anyone was wondering, or has the same problem as me). I was too focused on thinking what information a "no" answer to the question posed in (A) would give us versus what information a "yes" answer would give us.

Answering "no" to (A), that is, the average life of LEDs is NOT at least as long as that of incandescent bulbs, doesn't give us any information because the stimulus allows for there to be a situation in which the average life of LEDs is SHORTER and the cost is STILL minimized through the low energy consumption of LEDs and the cost of the LEDs themselves (as icefrog notes). The reason for this is that we don't know how much lower the energy consumption is or how much lower the costs are of LEDs versus incandescent bulbs so we can't rule out a situation in which the low energy consumption and cost factors outweigh the shorter life span of LEDs as compared to incandescent bulbs; meaning, LEDs have shorter lives but still minimize the average yearly costs of Traverton. By the same logic, we also cannot rule out a situation in which the shorter life span of LEDs outweighs the lower energy consumptions and cost of LEDs as compared to incandescent light bulbs; meaning, LEDs have shorter lives and do not minimize the average yearly costs of Traverton. As a result, a "no" answer to (A) doesn't give us any additional information and neither confirms nor denies our belief that LEDs will minimize yearly annual costs.

On the other hand, a "yes" answer to (A) gives us additional information and serves to reaffirm our belief that LEDs will minimize yearly annual costs. If the average life span of LEDs is at least as long as that of incandescent bulbs then, based on the stimulus, it is a reaffirmation that they will result in minimized costs because that is in addition to the lower energy consumption and cost of the LEDs themselves serving to minimizing costs.

This was a great lesson for me and I feel like encountering this question without any context and on an actual test, it should maybe even be a medium difficulty, but that's just my opinion.

Also GMAT Experts please jump in with your thoughts regarding this analysis, I would be happy to read any additional pointers/analysis.

Hi Experts,
VeritasKarishma GMATNinja

I understand that A is useful to determine switching to LED is a good idea.

I usually get confused with variance test.

(A) Whether the expected service life of LED arrays is at least as long as that of the currently used incandescent bulbs
If we consider YES - The expected service life of LED arrays is at least as long as that of the currently used incandescent bulbs. It will strengthen the argument considering other benefits of LED (energy efficient, same purchase cost)
If we consider NO - The expected service life of LED arrays is NOT at least as long as that of the currently used incandescent bulbs. The life can be shorter or longer. It will strengthen or weaken the argument depending on the answer.
What's the negation of "At least as long as"?
Thanks!