Per unit, compact fluorescent light bulbs (CFLs) are slightly more

Hi pavankarwa123,
Hi we can say that cfl uses less energy than incandescent lights but we cant comment on the households.
May be the CFL households use more number of lights thus using more energy... so we cannot be sure about the statement

As per question "and thus provide the ability to save money on energy expenses over the long run. "

Cost of CFL is high at the same time it energy consumption is low , this fact is to be compared with incandescent light bulbs
and we have to tell how we can save money.

pre thinking : Incandescent bulb ( Manufac.. cost + Energy cost ) >> CFL ( Manufac.. cost + Energy cost ) so we can save money
We know that : Incandescent bulb ( Manufac.. cost ) << CFL ( Manufac.. cost)
So the energy cost of Incandescent bulb should be high such that becomes greater than CFL ( Manufac.. cost + Energy cost )
Option A exactly is as per our thinking
Ⓑ CFLs are now as readily available as incandescent light bulbs at most major retailers, including online vendors. - Availability OUT of scope
Ⓒ Incandescent light bulbs are compatible with a greater number of light fixtures than are CFLs.
We are not concerned about its compatibility
Ⓓ Households equipped with CFLs use less energy than households equipped with incandescent light bulbs. Close answer , but have a major flaw house holds will not have only CFL or incan.. bulbs , there are lot off other equipments which is used also to be taken into account.
Ⓔ The primary material from which CFLs are manufactured is slightly more expensive than the primary material used to manufacture incandescent light bulbs. irrelevant , we have to tell how in long run CFL will save money. this option explains about manufacturing cost.

[quote="EMPOWERgmatMax"]CR INFERENCE SERIES: Question 2) Per Unit, Compact Fluorescent Light Bulbs

Per unit, compact fluorescent light bulbs (CFLs) are slightly more expensive to produce than incandescent light bulbs, and CFLs also sell at a noticeable premium over comparable incandescent light bulbs. However, CFLs are less expensive overall than incandescent light bulbs because CFLs typically use 75% less electricity to operate, and thus provide the ability to save money on energy expenses over the long run.

Text in red: Counter premises
Text in blue: Premise
Text in green: Conclusion

In must be true (or inference) questions, the correct answer choice is always true and not might be true. Additionally, prethinking in these questions is difficult as an inference can be based on 1 or more than 1 premises. So we will now straightaway do the POE of the given choices based on above.

The above statements, if true, most strongly support which of the following?

Ⓐ The additional energy cost from use of incandescent light bulbs instead of CFLs exceeds the additional manufacturing cost associated with the production of CFLs.
Correct. The given premises mention that in the longer run, CFLs are more economical than the incandescent lightbulbs. This has to be true for the total cost for the end user to be lower in the longer run despite higher manufacturing and selling costs.

Ⓑ CFLs are now as readily available as incandescent light bulbs at most major retailers, including online vendors.
Incorrect. This might be true but the argument provides no information about the availability

Ⓒ Incandescent light bulbs are compatible with a greater number of light fixtures than are CFLs.
Incorrect. This might be true but the argument provides no information about the compatibility of incandescent light bulbs.

Ⓓ Households equipped with CFLs use less energy than households equipped with incandescent light bulbs.
Incorrect. This might be true but is not a must be true. The given argument talks about the efficiency of CFL bulbs in the longer run, but nowhere does the argument talk about household or industrial or any other particular application. This option can be made false by assuming that people in households equipped with CFL bulbs to be efficiency conscious. How about they install more CFL bulbs than necessary and in effect lead to similar electricity bills.

Ⓔ The primary material from which CFLs are manufactured is slightly more expensive than the primary material used to manufacture incandescent light bulbs.
Incorrect. Material importance (whether the 'primary' material is more expensive or the 'secondary'?) is not mentioned in the argument. All we know that the cost for manufacturing CFL bulbs are slightly more than that for manufacturing incandescent bulbs. This higher manufacturing cost can be due to the material used or the technology used to manufacture these bulbs. The argument does not go into details about the reasons for increase in the manufacturing costs.

CR INFERENCE SERIES: Question 2) Per Unit, Compact Fluorescent Light Bulbs

Per unit, compact fluorescent light bulbs (CFLs) are slightly more expensive to produce than incandescent light bulbs, and CFLs also sell at a noticeable premium over comparable incandescent light bulbs. However, CFLs are less expensive overall than incandescent light bulbs because CFLs typically use 75% less electricity to operate, and thus provide the ability to save money on energy expenses over the long run.

The above statements, if true, most strongly support which of the following?

Ⓐ The additional energy cost from use of incandescent light bulbs instead of CFLs exceeds the additional manufacturing cost associated with the production of CFLs.
Ⓑ CFLs are now as readily available as incandescent light bulbs at most major retailers, including online vendors.
Ⓒ Incandescent light bulbs are compatible with a greater number of light fixtures than are CFLs.
Ⓓ Households equipped with CFLs use less energy than households equipped with incandescent light bulbs.
Ⓔ The primary material from which CFLs are manufactured is slightly more expensive than the primary material used to manufacture incandescent light bulbs.

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Official Explanation

Question Type: Inference
Boil It Down (Simplified & Abbreviated Summary of the Prompt): CFL more $, but saves $ in long run.
Goal: Select the option that has to be 100% logically true from the prompt
Analysis: This is a straightforward Inference question. We need to find an option that follows with 100% certainty. In Inference questions, GMAC can be expected to deliver 2 types of incorrect options:

1) Those that are too extreme to be supported from the facts given
2) Options that seem reasonable, but are not supported from the facts given

Ⓐ The additional energy cost from use of incandescent light bulbs instead of CFLs exceeds the additional manufacturing cost associated with the production of CFLs.
Yes! This option has to be 100% true. We know that CFLs save enough energy to make them financially advantageous over incandescent lightbulbs, despite the higher cost of CFLs. Therefore, the ONLY way that could be possible is if the additional energy cost from use of incandescent light bulbs instead of CFLs exceeds the additional manufacturing cost associated with the production of CFLs.

Ⓑ CFLs are now as readily available as incandescent light bulbs at most major retailers, including online vendors.
No idea. We’re only allowed to go by this prompt, and on the basis of this prompt, we have no clue whatsoever as to how readily available CFLs are. Gone.

Ⓒ Incandescent light bulbs are compatible with a greater number of light fixtures than are CFLs.
No idea either. We have absolutely zero ability to comment the volume of fixtures that are compatible with incandescent light bulbs or CFLs. Gone.

Ⓓ Households equipped with CFLs use less energy than households equipped with incandescent light bulbs.
This is absolutely the runner up option, and this is another fantastic example of how reading with an intense eye for GMAC’s twists will pay off. Why is this option wrong: HOUSEHOLD energy use. How on earth can we comment on overall household energy use just from the information as to whether they use CFLs or incandescent bulbs? There’s just no way. Maybe those who use CFLs also tend to have a higher likelihood of owning electric cars, and so their overall electric consumption is higher than CFL households. What if CFL users are more likely to own homes in the desert and use an far greater amount of electricity on air conditioning? So you see, even though this option MIGHT be true, and is probably true, there is no way to know that it IS TRUE. Gone.

Ⓔ The primary material from which CFLs are manufactured is slightly more expensive than the primary material used to manufacture incandescent light bulbs.
Even though CFLs are slightly more expensive to manufacture than incandescent light bulbs, there is no way to attribute that difference to the PRIMARY MATERIAL. Maybe the difference can be attributed to a greater labor expense, or maybe CFLs use more energy to manufacture. Gone.

All in, this question showcases the key difference in Inference questions between options that can be true vs. the one that MUST BE TRUE. That difference is essential to ace the 4 RC Inference questions that you’re likely to see in RC, and the 2 CR Inference questions that you’re likely to see on your real GMAT.


◀ CR INFERENCE SERIES: Question 1) Securities Industry Regulator

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Hi pavankarwa123,

You raised the KEY QUESTION here. It looks like in addition to the official explanation, which I've just shared, others have addressed the exact same aspect of this question. If you still have any follow questions, please feel free to either ask here, or PM me. Nice job answering the question successfully and spotting the tricky nature of D in this question (similar to the observation you mentioned in the last question in the series).

Hi Engr2012,

FANTASTIC work here! I enjoyed your thorough breakdown. I hope that you're continuing to breakdown all of the questions you're practicing just like this. The long-term gain from such thoughtful analysis will be astounding.

Need to decide between A and D...
The word 'instead' in option A,=> exact replacement(100 incand.=>100CFC)
but in option D, the number is not discussed. so can be more or less based on occasion

Hi gocoder,

I'd be happy to help. Here's the key distinction: understanding exactly what GMAT Inference questions are asking you to do.

The concept of an inference as it appears on the GMAT is widely misunderstood. People often think that Inference questions are asking them to look for something reasonable/generally agreeable as could appear to be the case here with option D, but on the GMAT, options that are VERY reasonable but not 100% supported are incorrect. GMAT Inference questions are seeking to measure whether you can determine which option can be factually determined, as we can with option A, and which ones we can't (all the other options). GMAT Inference questions will directly reward you for that distinction.

Ⓐ The additional energy cost from use of incandescent light bulbs instead of CFLs exceeds the additional manufacturing cost associated with the production of CFLs.
yes, this one must be true, otherwise the argument is not valid.

Ⓑ CFLs are now as readily available as incandescent light bulbs at most major retailers, including online vendors.
irrelevant

Ⓒ Incandescent light bulbs are compatible with a greater number of light fixtures than are CFLs.
irrelevant

Ⓓ Households equipped with CFLs use less energy than households equipped with incandescent light bulbs.
well, we can't know...what if energy is spent on smth that does not require light bulbs?

Ⓔ The primary material from which CFLs are manufactured is slightly more expensive than the primary material used to manufacture incandescent light bulbs.
irrelevant.

A is the answer.

hi ,
I agree with the explaination of D that more cfl may be installed but the stimulus says that " it is expencive to produce" not "manufacture ". there may be many reasons that can be attributed to expensive product. like manufacturing cost or costly raw material etc.therefore i counldnt agree with both A & E also. please clear the confusion...

the higher premium and the additional costs to produce CFLs are the same thing, so A is still a solid answer.

A.Now since from the stimuli,the overall cost of getting and using a CFL bulb is lesser than getting a comparable incandescent bulb,it means that the cost of energy for CFL+ price of CFL <cost of incandescent + cost of energy for incandescent. We know that the incandescent has a cheaper price so for the overall cost of the incandescent to exceed the overall cost of the CFL,its energy cost should be bigger than CFL's energy cost as well as CFL's additional manufacturing cost.

B.The stimuli does not support this.Remember,you can not introduce additional information into the answer choices rather than what is explicitly written in the stimulus or what can be inferred from the stimulus

C.Again the stimuli does not even touch this and it is out or scope for the same reason as B

D.Now this is the pitall. Incandescents use more energy,that is true but does it mean households who use incandescents consume more energy.What if households with CFLs run equipment that makes their energy consumption much greater than households with incandescent. So this could be true but its not definitely true

E. Could be true or could not.Maybe what makes CFLs more expensive is comparative labor costs for producing a unit of CFL and not the material.

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