GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 12 Nov 2018, 16:38

### 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

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

## Events & Promotions

###### Events & Promotions in November
PrevNext
SuMoTuWeThFrSa
28293031123
45678910
11121314151617
18192021222324
2526272829301
Open Detailed Calendar
• ### Essential GMAT Time-Management Hacks

November 14, 2018

November 14, 2018

08:00 PM MST

09:00 PM MST

Join the webinar and learn time-management tactics that will guarantee you answer all questions, in all sections, on time. Save your spot today! Nov. 14th at 7 PM PST

# M23-14

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 50544

### Show Tags

16 Sep 2014, 00:18
00:00

Difficulty:

35% (medium)

Question Stats:

67% (00:56) correct 33% (01:33) wrong based on 125 sessions

### HideShow timer Statistics

If line $$y=kx+b$$ is parallel to line $$x=b+ky$$, which of the following must be true?

A. $$k = b$$
B. $$k=b+1$$
C. $$b + k = 0$$
D. $$|k| - 1 = 0$$
E. $$k = -k$$

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 50544

### Show Tags

16 Sep 2014, 00:18
1
2
Official Solution:

If line $$y=kx+b$$ is parallel to line $$x=b+ky$$, which of the following must be true?

A. $$k = b$$
B. $$k=b+1$$
C. $$b + k = 0$$
D. $$|k| - 1 = 0$$
E. $$k = -k$$

For lines to be parallel, their slopes must be equal.

The second equation can be rewritten as $$y=\frac{1}{k}*x-\frac{b}{k}$$ and since the slopes of two lines must be equal, then it must be true that $$k=\frac{1}{k}$$ or $$k^2=1$$ or $$|k|=1$$.

_________________
Intern
Joined: 19 Dec 2015
Posts: 28

### Show Tags

23 May 2016, 10:26
This is a very good question in my opinion, should be bumped for further review and discussion
Intern
Joined: 13 Oct 2017
Posts: 39

### Show Tags

17 Oct 2017, 05:42
Hi guys,

I'm still a little confused...I tried plugging in either x or y in order to get the required answer and failed miserably...can Bunuel et al give a more granular explanation please?

Thanks
Math Expert
Joined: 02 Sep 2009
Posts: 50544

### Show Tags

17 Oct 2017, 06:29
1
ttaiwo wrote:
Hi guys,

I'm still a little confused...I tried plugging in either x or y in order to get the required answer and failed miserably...can Bunuel et al give a more granular explanation please?

Thanks

Can you please tell me what is unclear in the solution? Thank you.
_________________
Intern
Joined: 13 Oct 2017
Posts: 39

### Show Tags

17 Oct 2017, 11:28
Bunuel wrote:
ttaiwo wrote:
Hi guys,

I'm still a little confused...I tried plugging in either x or y in order to get the required answer and failed miserably...can Bunuel et al give a more granular explanation please?

Thanks

Can you please tell me what is unclear in the solution? Thank you.

Thanks for your response...I did the second substitution as you said but ended up with:

y = x-b/k ...even tried to expand that even further...and got y= x/k - b/k

In effect I don't know how you ended up with:

y=1/k∗x−b/k

I don't know where the 1/k is coming from.
Math Expert
Joined: 02 Sep 2009
Posts: 50544

### Show Tags

17 Oct 2017, 20:00
ttaiwo wrote:
Bunuel wrote:
ttaiwo wrote:
Hi guys,

I'm still a little confused...I tried plugging in either x or y in order to get the required answer and failed miserably...can Bunuel et al give a more granular explanation please?

Thanks

Can you please tell me what is unclear in the solution? Thank you.

Thanks for your response...I did the second substitution as you said but ended up with:

y = x-b/k ...even tried to expand that even further...and got y= x/k - b/k

In effect I don't know how you ended up with:

y=1/k∗x−b/k

I don't know where the 1/k is coming from.

$$x=b+ky$$;

Re-arrange: $$x - b=ky$$;

Divide by k: $$\frac{x}{k} - \frac{b}{k}=y$$.

Notice that $$\frac{x}{k}$$ is the same as $$\frac{1}{k}*x$$.
_________________
Intern
Joined: 30 Mar 2018
Posts: 7
Location: India
Concentration: Sustainability, General Management
Schools: Erasmus '20
GMAT 1: 550 Q44 V23
GMAT 2: 660 Q44 V38
GMAT 3: 710 Q47 V41
GPA: 3
WE: Architecture (Other)

### Show Tags

15 Apr 2018, 02:23
ttaiwo

$$\frac{x-b}{k}$$ = $$\frac{x}{k}$$ - $$\frac{b}{k}$$

since $$\frac{x}{k}$$ = $$\frac{1}{k}$$ * $$x$$,

$$y = \frac{1}{k} * x - \frac{b}{k}$$
Re: M23-14 &nbs [#permalink] 15 Apr 2018, 02:23
Display posts from previous: Sort by

# M23-14

Moderators: chetan2u, Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.