Q. Is ABC an equilateral triangle?

Expert replies

Previous Topic Next Topic

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

by BTGmoderatorDC » Thu Jul 04, 2019 7:33 pm

Timer

00:00

Answers

Stats

Difficulty—

Q. Is ABC an equilateral triangle?

1. âˆ ABC = âˆ ACB

2. Length of AB = Length of AC and one of the angles of the triangle is 60 degrees

OA B

Source: e-GMAT

Like this post

Source: Beat The GMAT — Data Sufficiency | Thu Jul 04, 2019 7:33 pm

GMAT/MBA Expert

Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Fri Jul 05, 2019 3:01 am

Statement 1 alone only ensures the triangle is isosceles.

From Statement 2, two sides are equal, so two angles must be equal. We also know one angle is 60 degrees. If that's one of the two equal angles, we have two 60 degree angles, and the third angle then must also be 60 degrees (because a triangle's angles sum to 180 degrees), and our triangle is equilateral. If that 60 degree angle is not one of the two angles we know to be equal, then those two equal angles need to sum to 120, and they are thus both 60 degrees, and again our triangle is equilateral. So Statement 2 is sufficient.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

Like this post

deloitte247: Legendary Member; Posts: 2214; Joined: Fri Mar 02, 2018 2:22 pmFollowed by: 5 members

by deloitte247 » Sat Jul 06, 2019 2:14 pm

Statement 1=> âˆ ABC = âˆ ACB
There is no specific information about the sides for angles. Hence, statement 1 is INSUFFICIENT.

Statement 2=> Length of AB = Length of AC, and one of the angles of the triangle is 60 degrees.
For a triangle to have 2 equal sides, it means it has 2 equal angles, and with the third angle being 60 degrees.
$$180=60+\frac{120}{2}+\frac{120}{2}$$
$$180=60+60+60$$
Hence, it is an equilateral triangle. Statement 2 alone is SUFFICIENT.

The correct answer is OPTION B

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

563 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (563 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review