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# The diagram shows, in three column groupings, various divisions of Ear

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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
yatesri wrote:

It's my first post here although I often read your forums. I tried an integrated reasoning problem for the first time today and for the most part did fine. However, I'm confused by the answer on this sample problem from the GMAT site:

The board won't allow me to post pictures but the question is from the official GMAT site's integrated reasoning sample questions.

Attachment:
GID1023.gif
The diagram shows, in three column groupings, various divisions of Earth's geological history since its formation approximately 4,600 million years ago. In the leftmost column grouping, the Precambrian eon is subdivided into chronometric eons shown on the far left; but otherwise, in the rest of the graphic, each subsequent column to the right shows the subdivisions of the timeframes to its left. Each of the rightmost two column groupings is a magnification—with additional information—of a portion of the grouping directly to its left.

Fill each blank using the drop-down menu to create the most accurate statement on the basis of the information provided.

The Miocene epoch spans closest to (3%, 25%, 85%) of the era of which it is a part.

According to the diagram the beginning of the (Cambrian period, Triassic Period, Pliocene Epoch, Precambrian eon) marks the onset of a new eon, era, and period in geological history.

25%, Cambrian Period

I'm confused by the answer to the second question. The beginning of the Cambrian period does not coincide with the onset of a new eon, era, and period. If I'm reading it wrong, I apologize for wasting your time.

Hi,

Though I am not sure where your confusion lies but let me have a try.

Basically, if you look at the first figure from the left, you can see that there are only two eons: Precambrian and Phanerozoic.

However, there is no information about eras or periods at the beginning of Precambrian eon.

So, the only solution possible which can start with eon, era and period, will be the one starting with Phanerozoic eon.

Now that is the case with Cambrian period. For this, Phanerozoic eon starts, Paleozoic era starts and Cambrian period starts. Therefore, this is the correct answer.

In addition, you can see that the answer also could have been Phanerozoic eon. (same three times start in this case also).

Hope this helps

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Chiranjeev
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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
3
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egmat wrote:
Hi,

Though I am not sure where your confusion lies but let me have a try.

Basically, if you look at the first figure from the left, you can see that there are only two eons: Precambrian and Phanerozoic.

However, there is no information about eras or periods at the beginning of Precambrian eon.

So, the only solution possible which can start with eon, era and period, will be the one starting with Phanerozoic eon.

Now that is the case with Cambrian period. For this, Phanerozoic eon starts, Paleozoic era starts and Cambrian period starts. Therefore, this is the correct answer.

In addition, you can see that the answer also could have been Phanerozoic eon. (same three times start in this case also).

Hope this helps

e-GMAT has recently launched a full fledged course on IR encompassing 15+ hours of interactive audio visual content, 35 concepts, 120+ original questions, and 2 full length Mock Tests. Visit e-gmat for a free trial.

Thanks,
Chiranjeev

What is confusing for me is that the answer states that "According to the diagram the beginning of the Cambrian period marks the onset of a new eon, era, and period in geological history.

However, according to the expanded graph to the right, the beginning of the Cambrian period does not mark the onset, the end of the Cambrian period does.

This is also the beginning of the Precambrian Era; also an answer choice.

Doesn't the question wording prevent the Cambrian period from being a correct answer?

Thanks,
yatesri
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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
A) 25% per the third graph (Magnified version)

B) Cambrian period per the second graph ( Magnified version)

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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
Official Explanation

According to the rightmost column of the diagram, the Miocene epoch spans 17 million years, from about 6 million to 23 million years ago. The rightmost column also represents the entire Cenozoic era that appears in the middle column and spans 65 million years. Dividing 17 by 65 yields approximately 0.262, or 26.2%, which is closest to the menu option of 25%.

The only place in the diagram that distinctly represents eons, eras, and periods together is in the middle column, and the only place in the middle column where there is a dividing line common to an eon, era, and period is at the beginning of the Cambrian period at about 550 million years ago.

The correct answer is Cambrian period.
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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
What was confusing to me is that zero is "the present" whereas 4600 is in the past. Is there a rule of thumb stating that generally historical graphs graphs count years up (up to BC I would assume)?
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Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
The graph is meant to be read from bottom people. 0 years ago is the most recent, 10 years ago is less recent and so on. Keep that in mind.
Re: The diagram shows, in three column groupings, various divisions of Ear [#permalink]
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