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In quadrilateral ABCD, what is the value of angle ADC?

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Manager
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In quadrilateral ABCD, what is the value of angle ADC?  [#permalink]

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New post 13 Dec 2014, 16:50
3
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A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

74% (01:06) correct 26% (01:17) wrong based on 139 sessions

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In quadrilateral ABCD, what is the value of angle ADC?

(1) Angle BAD + Angle ABC + Angle BCD = 280
(2) Angle BAD + Angle ADC + Angle BCD = 300
Manager
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Re: In quadrilateral ABCD, what is the value of angle ADC?  [#permalink]

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New post 13 Dec 2014, 16:53
1
I think you don´t need to do any calculation or even draw a diagram for this problem. Just use your common sense.

- Remember that the sum of the interior angles of any quadrilateral is 360º.
- The question asks for the value of a specific angle of the four (angle ADC)
- You can´t assume that other angle/s has/have the same value as ADC has since you don´t know whether this quadrilateral is a square, rectangle, rhombus, or any other type of quadrilateral.

(1) Statement 1 says: All the other 3 angles = 280. Therefore, ADC must equal 80. Sufficient.

(2) Statement 2 has a similar format but says: 2 of the angles + ADC = 300. You can´t know what ADC is since ABC is now not included in this equation. Insufficient.


Takeaways from this question
- Know your Geometry formulae cold
- Don´t assume things away (especially in DS Geometry)
- Be aware of DS Combo Questions
- Be aware of similar-format statements. One could be sufficient and the other insufficient!
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Re: In quadrilateral ABCD, what is the value of angle ADC?  [#permalink]

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New post 16 Sep 2017, 20:36
minwoswoh wrote:
I think you don´t need to do any calculation or even draw a diagram for this problem. Just use your common sense.

- Remember that the sum of the interior angles of any quadrilateral is 360º.
- The question asks for the value of a specific angle of the four (angle ADC)
- You can´t assume that other angle/s has/have the same value as ADC has since you don´t know whether this quadrilateral is a square, rectangle, rhombus, or any other type of quadrilateral.

(1) Statement 1 says: All the other 3 angles = 280. Therefore, ADC must equal 80. Sufficient.

(2) Statement 2 has a similar format but says: 2 of the angles + ADC = 300. You can´t know what ADC is since ABC is now not included in this equation. Insufficient.


Takeaways from this question
- Know your Geometry formulae cold
- Don´t assume things away (especially in DS Geometry)
- Be aware of DS Combo Questions
- Be aware of similar-format statements. One could be sufficient and the other insufficient!




Basic question:

How do we draw this quadrilateral?
We could label nodes in different orders and the whole meaning of the angles would be different. Is there a convention line the letters are in order in clockwise?

Let's say we have two nodes on top and two lower: lower left node could be C or D. How do we know what is assumed by the question?
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Re: In quadrilateral ABCD, what is the value of angle ADC?  [#permalink]

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New post 21 Mar 2019, 05:37
minwoswoh wrote:
I think you don´t need to do any calculation or even draw a diagram for this problem. Just use your common sense.

- Remember that the sum of the interior angles of any quadrilateral is 360º.
- The question asks for the value of a specific angle of the four (angle ADC)
- You can´t assume that other angle/s has/have the same value as ADC has since you don´t know whether this quadrilateral is a square, rectangle, rhombus, or any other type of quadrilateral.

(1) Statement 1 says: All the other 3 angles = 280. Therefore, ADC must equal 80. Sufficient.

(2) Statement 2 has a similar format but says: 2 of the angles + ADC = 300. You can´t know what ADC is since ABC is now not included in this equation. Insufficient.


Takeaways from this question
- Know your Geometry formulae cold
- Don´t assume things away (especially in DS Geometry)
- Be aware of DS Combo Questions
- Be aware of similar-format statements. One could be sufficient and the other insufficient!


Thank you for the takeaway.

Action item for me: dont get intimidated by geometry questions, especially because I am so used to solving the types of geometry questions where a figure or a shape is given.

Room for improvement: I spent too much time trying to figure-out things that are not helpful at all, given the question asked.

Eg I stalled because I dont know how to draw this quadrilateral. In fact, dare I say that "forcing" this problem to be graphed on my paper is not only not helpful; it makes the problem more complex because my brain is distracted on the wrong thing, such as " I wonder if this figure is a square or a rhombus ? ".

In the forthcoming exam, I need to be more comfortable with solving abstraction (even for Geometry-type of problem).

Hope this help the GMATClub community.
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Re: In quadrilateral ABCD, what is the value of angle ADC?  [#permalink]

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New post 25 Sep 2019, 00:28
The trap here is with B - don't assume its a parallelogram and that opposite sides are equal.
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Re: In quadrilateral ABCD, what is the value of angle ADC?   [#permalink] 25 Sep 2019, 00:28
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In quadrilateral ABCD, what is the value of angle ADC?

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