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# Scientists have dated sharp-edged flakes of stone found in

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Magoosh GMAT Instructor
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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09 Dec 2012, 15:10
1
ziko wrote:
Thanks Mike,
Your answer is very good. But does it mean that i always should avoid "empty it"? (of course whenever i am faced to two grammatically and logically correct answers).

Don't mechanically avoid the "empty it" --- nothing in grammar is completely mechanical. Most often, you will notice that the "empty it" phrasing is longer, wordier, less clear, less concise, less powerful. Most often, if two ways to say something are grammatically correct and one involves the "empty it", then then other will be more concise and more powerful. There are rare cases in which the most direct and efficient way to express something involves the "empty it." There are also GMAT SC problems in which four of the answers are incorrect, and the only possible correct answer involves an "empty it" --- remember, the answer to a GMAT SC question is going to be the best answer from among those five, not necessarily the very best way to express that idea. It will be grammatically correct, but not necessarily ideal.
Does all this make sense?
Mike
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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03 Jan 2013, 18:37
1
A. when it is known that humans made - when modifies "known", seems to suggest it was known 150,000 yrs ago
B. at which it is known that humans had made - same issue
C. at which humans are known to have made - correct answer
D. that humans are known to be making - known to be making is not crrect
E. of humans who were known to make - earliest date of humans doesnt make sense
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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01 Aug 2014, 00:47
'Dated at' is correct idiom , also sentence conveys correct meeting C wins
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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14 May 2015, 08:30
1
The original sentence has a meaning error. It seems to express that the "earliest date" is when something is known. This is not the intended meaning.
B also has the same kind of meaning error.
C removes the meaning ambiguity. - CORRECT.
D - "that" is a wrong pronoun to indicate time.
E - awkward.
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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14 May 2015, 21:03
Can someone pls explain the difference between:

Thanks
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31 May 2015, 18:23
mikemcgarry wrote:
What the sentence is trying to say ----- (a) humans made tools 2.6 Mya, and (b) right now, we know this to be the case. There are two actions, happening at different times --- the tool making (2.6 Mya) and the knowing about the tool-making (right now).

Look at thhe grammatical structure in (A).
.... the earliest date when it is known that humans made stone tools.
What precisely is happening at that "when"-time? Is it the knowing or the making? Technically, the clause that immediately follows "when" is "it is known", so grammatically, this would suggest the knowing happened at this "when"-time, 2.6 Mya. But logically, we know that's not the case --- it's not the "knowing" that happened 2.6 Mya, but rather the tool-making. The knowing is what the paleoanthropologists are doing right now.

Hello Mike -

I am trying to understand the logical mistake for (A) being wrong.

When it says "...pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools.

Doesn't it pushes back the date of knowing. Something like,

2.6mn Yrs|..............150k yrs..................|2.45mn yrs......................................................................|............150k yrs..................(push back out earliest date of knowledge).....|Now
<--------------------------------------------------------------------------------------------------------------------------------------------------Pushed back the date of knowing, which is wrong, and hence the wrong answer. Because author's intended meaning in this sentence is about updating our knowledge about first use of stone tools which we thought to be 2.45 mn years old but are actually 2.6 mn years old?

Regards
Sandeep
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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01 Jun 2015, 12:53
1
sandeepmanocha wrote:
mikemcgarry wrote:
What the sentence is trying to say ----- (a) humans made tools 2.6 Mya, and (b) right now, we know this to be the case. There are two actions, happening at different times --- the tool making (2.6 Mya) and the knowing about the tool-making (right now).

Look at thhe grammatical structure in (A).
.... the earliest date when it is known that humans made stone tools.
What precisely is happening at that "when"-time? Is it the knowing or the making? Technically, the clause that immediately follows "when" is "it is known", so grammatically, this would suggest the knowing happened at this "when"-time, 2.6 Mya. But logically, we know that's not the case --- it's not the "knowing" that happened 2.6 Mya, but rather the tool-making. The knowing is what the paleoanthropologists are doing right now.

Hello Mike -

I am trying to understand the logical mistake for (A) being wrong.

When it says "...pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools.

Doesn't it pushes back the date of knowing. Something like,

2.6mn Yrs|..............150k yrs..................|2.45mn yrs......................................................................|............150k yrs..................(push back out earliest date of knowledge).....|Now
<--------------------------------------------------------------------------------------------------------------------------------------------------Pushed back the date of knowing, which is wrong, and hence the wrong answer. Because author's intended meaning in this sentence is about updating our knowledge about first use of stone tools which we thought to be 2.45 mn years old but are actually 2.6 mn years old?

Regards
Sandeep

Dear Sandeep,
the earliest date when it is known that humans made stone tools
Let's think about the particular date discussed. This could be interpreted two ways:
1) on the date discussed, humans started making stone tools, or at least leaving tangible evidence for doing so; at some much later time, we figured out from the evidence when this date ways.
2) on the date discussed, it was the first time that humans in history every had awareness that stone tools had ever been used. Now, we take for granted that, at some point in the distant past, folks used stone tools, but at some point in civilization, this was a new discovery, and the date discussed is the date of this discovery.
Of course, what the author means to say is meaning #1, but the grammar doesn't not uniquely support that meaning. On the GMAT SC, we are not allowed to give a sentence the benefit of the doubt. A good sentence says exactly what it means and means exactly what it says, and version (A) does not do this.

Does this make sense?
Mike
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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24 Oct 2015, 07:02
mikemcgarry wrote:
ziko wrote:
Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools.
A. when it is known that humans made
C. at which humans are known to have made
D. that humans are known to be making
E. of humans who were known to make

Thanks Mike for good explanation. I have chosen B, and think it is grammatically correct, but again here as you have explained "it is known" refers to the time when we find out about it but not humans first tool making time. Am i correct or i missed anything?

Dear Ziko,
First of all, yes, there's the logic issue --- the "earliest date" --- does this refer to the earliest date of knowing or the earliest day of making stone tools. Like (A), (B) also doesn't resolve this ambiguity.
Furthermore, (B) using something called the "empty it" ---- the "it" in "it is know that humans had made stone tools" is a pronoun that doesn't refer to any antecedent. It doesn't refer to anything. It is purely a grammatical placeholder, and in that sense it is "empty" --- unlike most bonafide pronouns, this "it" refers to nothing --- it has no valid antecedent. The GMAT generally avoids the "empty it" --- once or twice, I have seen an OA on official material involving an "empty it", but the GMAT uses the "empty it" far more frequently to construct wordy indirect phrases for incorrect answer choices.

Consider these two sentences:
(1) It is known that early humans used stone tools.
(2) Early humans are know to have used stone tools.
Both are grammatically correct, but the GMAT would consider the second one more direct, more powerful, and therefore a much better answer than the first.
Be suspicious of the "empty it" wherever you see it --- even if it's grammatically correct, it is in all likelihood not the correct answer.

Does all this make?

Mike

Hi Mike,
Thanks for the justification regarding the essence of the sentence. Its much clear now. However, I have one question. When referring to a date or a time frame, I learnt that usage of 'when' is preferred over usage of 'which'. That's the sole reason I chose A over C. Can we use both at which and when while referring time? Help me out here please
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26 Oct 2015, 10:12
1
dipanjan_1988 wrote:
Hi Mike,
Thanks for the justification regarding the essence of the sentence. Its much clear now. However, I have one question. When referring to a date or a time frame, I learnt that usage of 'when' is preferred over usage of 'which'. That's the sole reason I chose A over C. Can we use both at which and when while referring time? Help me out here please

Dear dipanjan_1988,
My friend, I'm happy to respond.

Of course, it is never a problem to use "when" in reference to a date or time. As concerns the word "which," I would make this distinction. The word "which" by itself sounds extremely awkward.
. . . the day which he came. . .
That should be
. . . the day when he came. . .
So, by itself, "which" is atrociously wrong. BUT, in a preposition construction with "at" or "in" or "by" is perfectly correct and in fact typical of sophisticated writing.
. . . the date at which Prohibition took effect . . .
. . . the year in which Flaubert published Madame Bovary . . .
. . . the time by which Helen will have arrived in Croatia . . .

Those are not only correct: they actually sound more sophisticated than they would have if we used "when."

I would caution you that you cannot master GMAT SC simply by learning some mythical "complete list" of grammar rules. To achieve mastery, you have to read. See this blog:
http://magoosh.com/gmat/2014/how-to-imp ... bal-score/
By reading sophisticated writing, you will develop a sense for the kinds of structures that are typical of sophisticated English writing.

Does all this make sense?
Mike
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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12 Dec 2015, 14:13
The idiom, "dated at" has been used here. All the other forms involving date are wrong.
Hence we are left with options, B and C.
C. at which humans are known to have made

The logical meaning of the sentence is that, research has been conducted, and the finding of that research has predicted a date at which humans have made stone tools. But such a prediction could also be wrong. Hence, we must leave room for doubt.
In option B, it says that, "it is known", but in reality, it is not known, simply predicted with the data on hand.
In option C, we leave room for further speculation regarding the same, hence, option C implies the correct meaning.
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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15 Mar 2016, 05:45
1
iDisappear wrote:
Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments
of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million
years ago, pushing back by more than 150,000 years the earliest date when it is
known that humans made stone tools.
A. when it is known that humans made
C. at which humans are known to have made
D. that humans are known to be making
E. of humans who were known to make

Here 'when' is used as an adverb after an expression of time to mean 'at which'.
'Sunday is the only day when I can relax.
The action 'relax' takes place on Sunday.
In the problem the action 'is known' takes place at a particular point of time in the past. It is incorrect. The correct action is 'humans made stone tools'.
Therefore, I think it is correct to say 'when humans made stone tools', or 'when human are known to have made stone tools'.
Both the structures are absent in the options.
But we can replace 'when' with 'at which'.
So, we have the correct option C
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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04 Sep 2017, 11:46
this is one of those problems from which you can learn about the ways in which these sorts of constructions are used. indeed, it is precisely from these sorts of problems that you must learn about the niceties of these constructions, as the gmat's usage can, and does, sometimes vary from that of other sources.

in this sort of construction, i'm pretty sure that either "when" or "at which" would be acceptable. (clearly, the latter is acceptable -- it appears in the correct answer, after all -- but i wouldn't object to the former.)
if you want to get really subtle, i think (not 100% sure) that "the date when" is used for actual, precise calendar dates, whereas "the date at which" is used for the usually more vague dates of historical events, such as the one in this problem. but i'm sure the test is not going to depend on this sort of nuanced difference.

i think the real problem with the construction in choice (a) is that the clause following "when" is "it is known". in other words, that choice suggests that the fact is (was?) known at that date, an interpretation that clearly doesn't make sense in context.
in the correct answer, the "at which" is followed by a clause whose subject is "humans", and which describes the actual action that took place at that date. therefore, i think the idea is that this clause more accurately describes the chronology of the events: i.e., the toolmaking happened at that date, and the fact is known now.

as for your other question, this isn't really a perfect tense, because it's actually not a tense at all -- it's an infinitive.
probably the easiest way to go here is to remember this as an idiomatic usage of the construction "known to". if the action is in the present, then you use "known to VERB"; if the action is in the past, then you use "known to have VERBed". as far as i know, these are the only two possible forms.
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30 Sep 2017, 04:32
Here is how I eliminate options.

(A) when it is known that humans made (there is no reference for it)
(B) at which it is known that humans had made (same as error in option A)
(C) at which humans are known to have made (correct)
(D) that humans are known to be making (comes down to meaning here. Pushing back the date should refer to the time period humans made the tools. This says something else)
(E) of humans who were known to make (comes down to meaning here also. pushing back date of humans changes the meaning of the sentence)

Please correct me if I am wrong with my reasoning above.
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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04 Dec 2017, 20:52
Can anyone explain the differences between A and C plz.
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