In 1981 children in the United states

[RonPurewal]

Jeff has taught mathematics since he moved to LA.
---->This sentence implies that Jeff is still teaching math or not? I have no sense about it.

Same possible implications as "... for three years".

The server has performed well in the past 5 years.
----> This sentence signifies that the server is still in good performance now？

Same potential implications as "He has taught for three years."

Again, any reasonable sentence is going to present a further context.
e.g.,
The server has performed well for the past 5 years, but now we need a new one. No longer ambiguous.
The server has performed well for the past 5 years, so there's no need to buy a new one just yet. No longer ambiguous. Doesn't mean the same as the previous example.

[RonPurewal]

The server had performed well by 2010.
----> This sentence indicates that the server was in good performance at a point before 2010, but not so in 2010 and thereafter?

The combination of "performed well" and "by 2010" doesn't really make any sense.
"By (date)" is used for things that are, essentially, achievements or changes of state. It's hard to express the concept in general terms"”especially since I'm somewhat bad at expressing things in general terms in the first place"”but think about things that represent fundamental changes.
E.g.,
* graduating from school (once you graduate, you have a degree; before, you didn't)
* X grows bigger than Y (now it's bigger; before, it was smaller)
* meeting a performance requirement
* performing well enough to qualify for the Olympic Trials]

Consider in particular the last example. "Perform well" doesn't represent a fundamental change of state; "perform well enough to qualify" does (you don't have to re-qualify once you've qualified).

So, it would make sense to say things like these:
The scholarship was offered to graduate students who had graduated from their undergraduate institutions between 2000 and 2005.
Anyone who had not performed well enough to qualify for the Olympic Trials by December could no longer try out for the team.

Doesn't make sense with "performed well", unless a single good performance is enough to meet some criterion (e.g., the Olympic Trials example).

[RonPurewal]

The server had performed well until 2010.
---->This sentence indicates that the server had been in good performance continuously before 2010, but somehow fell to do so in 2010 and thereafter?

Yes, but that's an implication of "until" (i.e., not an implication of "had performed").

[RonPurewal]

Cayla had owned the house before her mother passed away.
----->Does that mean Cayla owned the house at a point before her mother died, but Cayla might not own the house at the moment her mother died?

The relationship between the two things here is unclear, so it's impossible to evaluate this sentence.

When you use "had ___ed" for the earlier of two events, you're implying one of two things.
1/ The earlier event continued up to the time of the later one (By the time I saw the doctor, I had been sick for 5 days);
2/ The earlier event had a definite impact on the later one (I did not eat at the restaurant, since I had already eaten at home).

If there is no such relationship, then "had ___ed" doesn't make sense. In that case, the past tense is normally used for both things (Before she became a fashion designer, Laura was an astrophysicist.)

There's not enough context to determine whether such a relationship exists between Cayla's home ownership and her mother's death. If there's some relationship (e.g., it's relevant to a case in probate court), then "had ___ed" works. If there's no such relationship, it doesn't work.

[RonPurewal]

in 1980 forty percent of East High School class graduated; by 1997 the figure had grown to 67%.
--> correct. this would mean that 67% of the '97 class graduated (which is what we mean).

Then I wonder does the above sentence mean the figure had reached 67% at some point before 1997, and then it might fell to a lower value at the end of 1997 and thereafter?

That interpretation isn't ruled out by the actual rules of the tense, but it's precluded by common sense. If this is the sole topic of the sentence, then, obviously, we would not want to write the wrong year.

If you're talking about a general qualification that might be met by different individuals at different times, though, then yes.

E.g., ("Pomeranians" are small dogs, if you don't know):
Pomeranians who have attained a body weight of fourteen pounds by the age of 1 year are classified as "throwback Pomeranians".
This is a general categorization, so, hitting the 14-pound mark at any point in the first year would qualify. A Pom that hits 14 pounds when it's eleven months old is a throwback Pom, as is a Pom that hits 14 pounds when it is only five months old.

On the other hand, if you were to write
Our Pomeranian had attained a weight of 14 pounds by the age of one year
... then "one year" should be the time when the dog actually hit the 14-pound mark. Otherwise there would be no reason in the world to write the sentence this way; you'd want to write it with the correct date.

[RonPurewal]

Ron, from your words, how come a mathematical quantity using past perfect tense can convey the idea intended , while an action using past perfect tense can not?

I don't understand. Please quote the post to which you're referring; thanks.

[RonPurewal]

And another question regarding Choice D.
In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores, compared with a figure of nearly six hours a week in 1997

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores, compared with nearly six hours a week in 1997

The first sentence is Choice D, the latter one is what listed by Joe.
What is the magic about the three words "a figure of " that makes Choice D grammatically incorrect but Joe's example grammatically correct? Ron, I've seen your explanation above about Choice D. But I just can't tell how it relates to Joe's example.

Grammar is a non-issue here.

"The figure of 6 hours a week" is a redundant construction.

"The figure", like "the number" or "the statistic", stands for the number. Either you write "the figure" or you write the actual figure, but not both.

E.g., In 1990 the population of Las Vegas was only about 400,000, but by 2010 that figure had grown to 1,200,000.

Here, you NEED to say "that figure" (or "that number", or whatever), because you clearly can't write something like "400,000 had grown to 1,200,000".

You could also just write "the population" again, but it's generally undesirable to repeat nouns unless it's absolutely necessary to do so.

[Haibara]

The server had performed well by 2010.
----> This sentence indicates that the server was in good performance at a point before 2010, but not so in 2010 and thereafter?

The combination of "performed well" and "by 2010" doesn't really make any sense.
"By (date)" is used for things that are, essentially, achievements or changes of state. It's hard to express the concept in general terms"”especially since I'm somewhat bad at expressing things in general terms in the first place"”but think about things that represent fundamental changes.
E.g.,
* graduating from school (once you graduate, you have a degree; before, you didn't)
* X grows bigger than Y (now it's bigger; before, it was smaller)
* meeting a performance requirement
* performing well enough to qualify for the Olympic Trials]

Consider in particular the last example. "Perform well" doesn't represent a fundamental change of state; "perform well enough to qualify" does (you don't have to re-qualify once you've qualified).

So, it would make sense to say things like these:
The scholarship was offered to graduate students who had graduated from their undergraduate institutions between 2000 and 2005.
Anyone who had not performed well enough to qualify for the Olympic Trials by December could no longer try out for the team.

Doesn't make sense with "performed well", unless a single good performance is enough to meet some criterion (e.g., the Olympic Trials example).

Ron，I think you are a born instructor. Many thanks.
Is what you explained above the exact reason why Choice A is wrong?

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores; by 1997 they had spent nearly six hours a week.

Since "spend nearly six hours a week", like ""perform well", doesn't represent a fundamental change of state or indicate accomplishment of a job or task along the timeframe, thus the combination of "had spent nearly six hours a week" and "by 1997" makes no sense here.

However, by contrast, Choice B below, with "figure grow to nearly six hours a week" indicating a fundamental change, makes sense here in the timeframe of "by 1997".

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores; by 1997 that figure had grown to nearly six hours a week.

Also, I want to know if such requirement of "a fundamental change of state " only applies to "by [date]", or there are other timeframes that require the corresponding verb to signify "a fundamental change of state"? I notice the example you gave in the quote about the "the scholarship" , which uses a timeframe "between 2000 and 2005". Besides, is "before [sth happened]" a timeframe that requires the verb in the main clause to represent a fundamental change of state?
Sorry for bothering you for so long about this question. Appreciate

[RonPurewal]

Ron，I think you are a born instructor.

Well, I've always liked to annoy people with unnecessarily long explanations of things. So, maybe.
(:

Many thanks.

Sure.

Is what you explained above the exact reason why Choice A is wrong?

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores; by 1997 they had spent nearly six hours a week.

Since "spend nearly six hours a week", like ""perform well", doesn't represent a fundamental change of state or indicate a difference along the timeframe, thus the combination of "had spent nearly six hours a week" and "by 1997" makes no sense here.

Yes.

However, by contrast, Choice B below, with "figure grow to nearly six hours a week" indicating a fundamental change, makes sense here in the timeframe of "by 1997".

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores; by 1997 that figure had grown to nearly six hours a week.

Also yes.

[RonPurewal]

Also, I want to know if such requirement of "a fundamental change of state " only applies to "by [date]", or there are other timeframes that require the corresponding verb to signify "a fundamental change of state"? I notice the example you gave in the quote about the "the scholarship" , which uses a timeframe "between 2000 and 2005". Besides, is "before [sth happened]" a timeframe that requires the verb in the main clause to represent a fundamental change of state?

Nah. "Before" just means "before", and so is equally capable of expressing simple sequences of actions. (e.g., I usually walk the dog before going to the gym.)

Take a look at some examples of "by (timeframe)". E.g., just search for something like "by Friday" or "by 1995" (with the quotes) on google, and then pay attention to the contexts in the search results.
With "by ____", you'll notice that _____ is consistently seen as some sort of cutoff date by which something must be done (You need to pay this bill by Friday, or late fees will be added).
Or, for retrospective things (like New City had become the country's biggest city by 1905), it's a transition date, as explained earlier.

For some things, it's even both. E.g., when you say that a Pom is a throwback if it achieves the weight of 14 pounds by the age of one year, that's both a transition point AND a cut-off date.

"Before" doesn't carry these connotations. It can carry them, but it's much more versatile.
("Versatile" is not always a good thing; the downside of "versatility" is that there's more potential ambiguity in a statement. Not tested on the GMAT, but, just something to think about.)

[RonPurewal]

Sorry for bothering you for so long about this question. Appreciate

Not "bothering me" at all. In fact, I never consciously thought about these issues at all until I wrote my replies in this thread. So, it's fascinating.

Honestly, I could go on and on and on about these things, because I just like languages a lot. But, at the end of the day, on here we're limited to talking about things that are actually relevant to the gmat exam.

[Haibara]

Ron, all of your explanation above are so insightful and so beneficial to me that I admire you.

Now I can generalise that by [date] could be used either as a cutoff date or a transition date.
If it is used as a cutoff date(deadline), then the corresponding verb in the clause has to assume a completion of a task or job, or achievement of a certain honour. In this situation, the action of the verb could happen at the exact [date] or at any point before the [date].
If it is used as a transition date, then the corresponding verb in the clause has to assume a fundamental change of state. In this situation, the action of the verb must happen at the exact [date]. Because if the fundamental change of state happened at a point before the [date], we don't bother to say by [date], instead, we could just use the precise day when the change of state actually occurred.

Again, thank you, Ron and MGMT team, very much.

[tim]

Let us know if you have any further questions.

[Haibara]

Ron, is my generalisation in the post prior to Tim's complete and accurate ?
Thanks very much.

[RonPurewal]

Ron, is my generalisation in the post prior to Tim's complete and accurate ?
Thanks very much.

I don't think I really understand it. Without examples, it's too abstract for me to grasp.

But"”from what I do seem to understand"”it doesn't seem to encompass everything already discussed here, depending on what you mean by a "transition date". As I mentioned before (see examples about Pomeranian dogs), if you are talking about an entire group of things"”all of which undergo some transition by a certain date"”then, no, they don't all have to change at the same time.

E.g.,
At the age of fourteen, Darlene met her future husband; by the age of eighteen, she had married him.
--> Okay, she got married at 18. Otherwise there'd be no sense in writing the sentence this way.

But...
All of Darlene's sisters had married by the age of 21.
This does not mean that all of her sisters had weddings at exactly the age of 21.