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# Is AB parallel to CD?

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Math Expert
Joined: 02 Sep 2009
Posts: 52905
Is AB parallel to CD?  [#permalink]

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07 Feb 2018, 20:18
00:00

Difficulty:

65% (hard)

Question Stats:

34% (01:43) correct 66% (01:09) wrong based on 40 sessions

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Is AB parallel to CD?

(1) a + b = 180°

(2) a + c + d + e = 360°

Attachment:

2018-02-08_0817.png [ 7.36 KiB | Viewed 984 times ]

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Re: Is AB parallel to CD?  [#permalink]

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07 Feb 2018, 20:29

Is AB parallel to CD?

(1) a + b = 180°
As a + b = 180° and b + d = 180(sum of angles in a straight line)
We can clearly say that a = d. Since the corresponding angles are equal,
we can say that AB is parallel to CD (Sufficient)

(2) a + c + d + e = 360°
d + e = 180° (Sum of angles in a straight line)
a + c + (d + e) = 360° -> a + c = 180°
Without knowing the individual angles, we cannot say AB is parallel
to CD (Insufficient) (Option A)
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Joined: 27 Dec 2017
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Re: Is AB parallel to CD?  [#permalink]

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07 Feb 2018, 20:34
A is sufficient:If we assume line are parallel then 180-a=b implies if a+b = 180 it's parallel
B is not sufficient as we only conclude a = b but for parallel line we need a+b =180

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Re: Is AB parallel to CD?   [#permalink] 07 Feb 2018, 20:34
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