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If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex

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If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 27 Dec 2015, 09:29
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If ℓ1 is parallel to ℓ2 in the figure above, which of the following expressions must equal 180?

I. a + b
II. c + e
III.c + d + e

A. I only
B. II only
C. III only
D. II and III only
E. I, II, and III

[Reveal] Spoiler:
Attachment:
2015-12-27_2126.png
2015-12-27_2126.png [ 13.81 KiB | Viewed 2593 times ]
[Reveal] Spoiler: OA

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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 27 Dec 2015, 21:09
Bunuel wrote:
Image
If ℓ1 is parallel to ℓ2 in the figure above, which of the following expressions must equal 180?

I. a + b
II. c + e
III.c + d + e

A. I only
B. II only
C. III only
D. II and III only
E. I, II, and III

[Reveal] Spoiler:
Attachment:
2015-12-27_2126.png



I. a + b
need e
False

II. c + e
need b
False

III.c + d + e
equals 180

C. III only
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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 29 Dec 2015, 10:08
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Hi All,

This question is built around a few essential 'line rules' that you need to know for Test Day:

1) When parallel lines are crossed by a third line, the corresponding angles are EQUAL.
2) When two lines 'criss-cross', opposite angles are EQUAL
3) The sum of the angles on one side of a line totals 180 degrees.

In this prompt, we're told that L1 and L2 are parallel, which means that....

Angle A = Angle C
Angle B = Angle D

Since the two non-parallel lines criss-cross....

Angle E = the angle directly across the line from it.

Using this information, you can deduce that the first two of the three Roman Numerals CANNOT total 180 degrees (because there is missing 'angle space' between the angles). Based on the answer choices, since those two options don't total 180 degrees, there's only one answer that could be correct...

Final Answer:
[Reveal] Spoiler:
E


You can prove that Roman Numeral 3 totals 180 degrees though (using the three rules I listed above).

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Rich
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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 10 Feb 2017, 11:04
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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 10 Feb 2017, 11:07
EMPOWERgmatRichC wrote:
Hi All,

This question is built around a few essential 'line rules' that you need to know for Test Day:

1) When parallel lines are crossed by a third line, the corresponding angles are EQUAL.
2) When two lines 'criss-cross', opposite angles are EQUAL
3) The sum of the angles on one side of a line totals 180 degrees.

In this prompt, we're told that L1 and L2 are parallel, which means that....

Angle A = Angle C
Angle B = Angle D

Since the two non-parallel lines criss-cross....

Angle E = the angle directly across the line from it.

Using this information, you can deduce that the first two of the three Roman Numerals CANNOT total 180 degrees (because there is missing 'angle space' between the angles). Based on the answer choices, since those two options don't total 180 degrees, there's only one answer that could be correct...

Final Answer:
[Reveal] Spoiler:
E


You can prove that Roman Numeral 3 totals 180 degrees though (using the three rules I listed above).

GMAT assassins aren't born, they're made
Rich


Hello Rich,

Apart from above mentioned rules, are there other rules as well that we need to remember on test day?
Thanks.
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Thanks & Regards,
Anaira Mitch

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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex [#permalink]

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New post 10 Feb 2017, 11:38
Hi anairamitch1804,

While there are additional 'line rules' worth knowing, they're based primarily on the rules that I listed in this prompt. For example, if you have a pair of criss-crossing lines, then the sum of all 4 angles will always be 360 degrees. You could come to THAT conclusion in a couple of different ways though... First, the two sides of the line are each 180 degrees, so adding 180 and 180 totals 360. Second, all of the angles around an individual point can be formed into a circle, and that is 360 degrees.

There aren't that many unique line rules that the GMAT could test you on though, and as a category they don't show up too often - so if you're looking to pick up big points in the Quant section, 'line rule' questions won't be what you need to focus on.

GMAT assassins aren't born, they're made,
Rich
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Contact Rich at: Rich.C@empowergmat.com

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Re: If ℓ1 is parallel to ℓ2 in the figure above, which of the following ex   [#permalink] 10 Feb 2017, 11:38
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