Last visit was: 23 Sep 2026, 12:10 It is currently 23 Sep 2026, 12:10
Home
Messages
Tests
Schools
Events
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 23 Sep 2026
Posts: 113,818
Own Kudos:
843,212
 [1]
Given Kudos: 111,779
Products:
GMAT Club Tests
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 113,818
Kudos: 843,212
 [1]
M70-13 03 Sep 2018, 03:50
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

65% (hard)

Question Stats:

43% (01:32) correct 57% (01:51) wrong based on 30 sessions

History

Date
Time
Result
Not Attempted Yet

If angle BDC is approximately 65°, what is the approximate value of x?


A. \(20\)
B. \(30\)
C. \(40\)
D. \(50\)
E. \(60\)
ShowHide Answer
Official Answer
C
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 23 Sep 2026
Posts: 113,818
Own Kudos:
843,212
Given Kudos: 111,779
Products:
GMAT Club Tests
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 113,818
Kudos: 843,212
M70-13 03 Sep 2018, 03:50
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Official Solution:


If angle BDC is approximately 65°, what is the approximate value of x?


A. \(20\)
B. \(30\)
C. \(40\)
D. \(50\)
E. \(60\)


We’ll go for PRECISE because we have all the information we need to solve the question.

Adding AD and DC together, we see that triangle ABC is made up of lines of lengths 3, 4, 5 – a Pythagorean triplet! This means ∠B = 90°. Next, since BC = DC, we know that ∠CDB = ∠BDC = 65°. This makes ∠C = 180 – 65 – 65 = 50°. Now that we have two of the triangle’s angles, we can see that ∠A = 180 – 90 – 50 = 40°.


Answer: C
avatar
vb1991
avatar
Joined: 18 May 2018
Last visit: 24 Jun 2019
Posts: 14
Own Kudos:
6
 [1]
Given Kudos: 1
Location: India
Concentration: Marketing, Strategy
Schools: DeGroote'21 (A)
GMAT 1: 730 Q49 V40
Schools: DeGroote'21 (A)
GMAT 1: 730 Q49 V40
Posts: 14
Kudos: 6
 [1]
M70-13 Updated on: 02 Oct 2018, 01:59
Originally posted by vb1991 on 01 Oct 2018, 14:34.
Last edited by vb1991 on 02 Oct 2018, 01:59, edited 1 time in total.
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
This is a very poor quality question.
avatar
Shobhit7
avatar
Joined: 01 Feb 2017
Last visit: 29 Apr 2021
Posts: 239
Own Kudos:
441
 [2]
Given Kudos: 148
Posts: 239
Kudos: 441
 [2]
M70-13 01 Oct 2018, 14:45
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
x= Angle A= Sin-1(3/5)= 36.9 degrees.

But, by manipulating angles, we get 50 degrees.

There is an error in the question.

Posted from my mobile device
User avatar
Helium
User avatar
Joined: 08 Jun 2013
Last visit: 01 Jun 2020
Posts: 451
Own Kudos:
827
Given Kudos: 118
Location: France
Schools: INSEAD Jan '19
GMAT 1: 200 Q1 V1
GPA: 3.82
WE:Consulting (Other)
Schools: INSEAD Jan '19
GMAT 1: 200 Q1 V1
Posts: 451
Kudos: 827
M70-13 01 Oct 2018, 22:29
Kudos
Add Kudos
Bookmarks
Bookmark this Post
vb1991
This is a very poor quality question and the answer is wrong.

Since the larger triangle is a 3-4-5 type Pythagorean triangle with angle B = 90°, then the following HAS to be true:

angle A = 30°
angle C = 60°
Show more

vb1991

Mate, not all right angle triangles have measure of angles : 30, 60 and 90.

All right angled triangle will follow Pythagoras Theorem. But for 30-60-90 type right triangle sides will be in ratio : 1 : \sqrt{3} : 2

Clearly, 3-4-5 do not follow above side ratio.

So, angles will not be in 30-60-90 form for 3-4-5 right triangle.

In fact for 3-4-5 right triangle corresponding angles are 36.87 - 53.13 - 90.

Hope this helps!!
avatar
vb1991
avatar
Joined: 18 May 2018
Last visit: 24 Jun 2019
Posts: 14
Own Kudos:
6
Given Kudos: 1
Location: India
Concentration: Marketing, Strategy
Schools: DeGroote'21 (A)
GMAT 1: 730 Q49 V40
Schools: DeGroote'21 (A)
GMAT 1: 730 Q49 V40
Posts: 14
Kudos: 6
M70-13 02 Oct 2018, 02:01
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Harshgmat
vb1991
This is a very poor quality question and the answer is wrong.

Since the larger triangle is a 3-4-5 type Pythagorean triangle with angle B = 90°, then the following HAS to be true:

angle A = 30°
angle C = 60°

vb1991

Mate, not all right angle triangles have measure of angles : 30, 60 and 90.

All right angled triangle will follow Pythagoras Theorem. But for 30-60-90 type right triangle sides will be in ratio : 1 : \sqrt{3} : 2

Clearly, 3-4-5 do not follow above side ratio.

So, angles will not be in 30-60-90 form for 3-4-5 right triangle.

In fact for 3-4-5 right triangle corresponding angles are 36.87 - 53.13 - 90.

Hope this helps!!
Show more

I conflated two separate concepts, my bad. Thanks for the explanation!

Posted from my mobile device
avatar
Architmahajan25
avatar
Joined: 21 Oct 2019
Last visit: 07 Nov 2019
Posts: 1
Posts: 1
Kudos: 0
M70-13 01 Nov 2019, 11:11
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Please explain how is ∠CDB = ∠BDC = 65°?
avatar
aleksandratucha
avatar
Joined: 25 Mar 2020
Last visit: 07 Oct 2021
Posts: 3
Given Kudos: 1
Posts: 3
Kudos: 0
M70-13 07 Apr 2020, 16:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Architmahajan25
Please explain how is ∠CDB = ∠BDC = 65°?
Show more

It's already given in the problem question that BDC is approximately 65°. Since CDB and BDC are even, CDB is also 65.
Moderator:
Bunuel
Math Expert
113818 posts