In the figure above, the angle marked at c has been created

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pmFollowed by: 23 members

by BTGmoderatorDC » Thu Feb 21, 2019 5:58 am

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In the figure above, the angle marked at c has been created by extending the base of the triangle, as shown. What is the sum of a, b, and c?

(1) a = 85
(2) b = 60

OA A

Source: Veritas Prep

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Source: Beat The GMAT — Data Sufficiency | Thu Feb 21, 2019 5:58 am

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Thu Feb 21, 2019 6:38 am

BTGmoderatorDC wrote:

In the figure above, the angle marked at c has been created by extending the base of the triangle, as shown. What is the sum of a, b, and c?

(1) a = 85
(2) b = 60

Since b and c form a straight line, b+c = 180.
Thus, the calculate a+b+c, we need to know the value of a.
Question stem, rephrased:
What is the value of a?

Statement 1:
SUFFICIENT.

Statement 2:
No information about a.
INSUFFICIENT.

The correct answer is A.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Thu Feb 21, 2019 6:42 am

BTGmoderatorDC wrote:

In the figure above, the angle marked at c has been created by extending the base of the triangle, as shown. What is the sum of a, b, and c?

(1) a = 85
(2) b = 60

Target question: What is the sum of a, b, and c?
This is a good candidate for rephrasing the target question.

Since angles on a line add to 180Â°, we already know that b + c = 180
We get: a + b + c = a + 180
So, in order to find the sum of a, b and c, we need only find the value of a
REPHRASED target question: What is the value of a?

Aside: Here's a video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

Statement 1: a = 85
Perfect! The answer to the REPHRASED target question is a = 85
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: b = 60
We have no information about a
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Answer: A

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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