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# In triangle ABC above, what is the measure of angle DBC ?

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Math Expert
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In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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24 Dec 2017, 00:54
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In triangle ABC above, what is the measure of angle DBC ?

(1) Triangle ABD is isosceles.
[Reveal] Spoiler: OA

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Kudos [?]: 139308 [0], given: 12783

Math Expert
Joined: 02 Sep 2009
Posts: 43312

Kudos [?]: 139308 [0], given: 12783

Re: In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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24 Dec 2017, 00:54
Bunuel wrote:

In triangle ABC above, what is the measure of angle DBC ?

(1) Triangle ABD is isosceles.

Similar question from OG: https://gmatclub.com/forum/in-triangle- ... 68281.html
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In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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24 Dec 2017, 03:07
IMO :B
statement1: Dont know what angle is equal to what.insuff
=> <ADB + 2x=180 (Linear Pair)
=> x=40.
=><DBC=180-80-80=20. Sufficient.

Waiting for OA

Last edited by Micky1005 on 24 Dec 2017, 04:42, edited 1 time in total.

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Re: In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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24 Dec 2017, 04:20
Bunuel wrote:

In triangle ABC above, what is the measure of angle DBC ?

(1) Triangle ABD is isosceles.

IMO answer should be "B". Awaiting OA

Statement 1: Even without knowing the fact given in statement 1, we can conclude that ABD=x. Thus this point is insufficient

Statement 2: 100=2x + DBC; also DBC=180-4x
=>2x=80 =>x=40; therefore, DBC=20. This is sufficient
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In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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24 Dec 2017, 13:03
Bunuel wrote:
Bunuel wrote:

In triangle ABC above, what is the measure of angle DBC ?

(1) Triangle ABD is isosceles.

Similar question from OG: https://gmatclub.com/forum/in-triangle- ... 68281.html

The interior angles of a triangle sum to 180.
An isosceles triangle has 2 equal angles that are equal sides.
Since $$DBC = 180 - (2x+2x)$$, all we need to do is find the value for $$x$$.

(1) Triangle ABD is isosceles. So, AB = BD or AB = AD, since we don't know which one we cannot find DBC, this is insufficient.

(2) Angle ADB = 100. Angles ADB + BDC = 180, so 100 + 2x = 180, 2x = 180 - 100, x = 40. To find DBC, this is sufficient.

Last edited by exc4libur on 25 Dec 2017, 11:12, edited 1 time in total.

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Re: In triangle ABC above, what is the measure of angle DBC ? [#permalink]

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25 Dec 2017, 02:39
IMO : B
(1) We don't know whether AB = BD or AB = AD
(2) We certainly know AB = BD => ADB = 100 = DBC + DCB = 180 - 2.2x + 2x => We can calculate x hence we will know DBC angle

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Re: In triangle ABC above, what is the measure of angle DBC ?   [#permalink] 25 Dec 2017, 02:39
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