If k is negative, which of the following must also be negati

Expert replies

Previous Topic Next Topic

alanforde800Maximus: Master | Next Rank: 500 Posts; Posts: 187; Joined: Tue Sep 13, 2016 12:46 am

by alanforde800Maximus » Sun May 13, 2018 4:51 pm

Timer

00:00

Answers

Stats

Difficulty—

If k is negative, which of the following must also be negative?

A) (-k)^2

B) (-1) k

C) 1 - k

D) k + 1

E) k - 1

Like this post

Source: Beat The GMAT — Problem Solving | Sun May 13, 2018 4:51 pm

GMAT/MBA Expert

Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 amFollowed by: 34 members; Location: Grand Central / New York; Thanked: 470 times

by Jay@ManhattanReview » Sun May 13, 2018 8:41 pm

alanforde800Maximus wrote:If k is negative, which of the following must also be negative?

A) (-k)^2

B) (-1) k

C) 1 - k

D) k + 1

E) k - 1

We are given that k is negative, and we have to find out which of the following must also be negative.

Let's take each option one by one.

A) (-k)^2

=> [-(-|k|)]^2

=> [|k|]^2

=> A positive number.

B) (-1)k

=> (-1)*(-|k|)

=> |k|

=> A positive number.

C) 1 - k

=> 1 - (-|k|)

=> 1 + |k|

=> A positive number.

D) k + 1

=> -|k| + 1

=> A negative number + A positive number

The result can be positive or negative depending on the value of k.

If |k| > 1, the result is that k + 1 is a negative number; however, if |k| < 1, the result is that k + 1 is a positive number. This is not a must-be-true condition.

E) k - 1

=> -|k| - 1

=> A negative number. The correct answer.

The correct answer: E

Hope this helps!

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New Haven | Doha | Stockholm | Pretoria | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

Like this post

GMAT/MBA Expert

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 » Mon May 14, 2018 7:51 am

alanforde800Maximus wrote:If k is negative, which of the following must also be negative?

A) (-k)^2

B) (-1) k

C) 1 - k

D) k + 1

E) k - 1

NOTE: this is one of those questions that require us to check/test each answer choice. In these situations, always check the answer choices from E to A, because the correct answer is typically closer to the bottom than to the top.

For more on this strategy, see my article: https://www.gmatprepnow.com/articles/han ... -questions

So, beginning with E...

E) k - 1
If we think of the number line, we know that, since k is NEGATIVE, it lies to the LEFT of zero on the number line.
When we subtract 1, we move one unit (space) to the LEFT.
So, since k already lies to the left of zero on the number line, when we move one more space to the left, we will STILL BE left of zero on the number line
This means k-1 must be negative.

Answer: E

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

swerve: Legendary Member; Posts: 2579; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Mon May 14, 2018 11:11 am

A. (-k)^2 --> (+ve)^2 --> +ve.

B. (-1)k --> (-ve)*(-ve) --> +ve.

C. 1 - k --> 1 - (-ve) --> 1 + ve --> +ve.

D. k + 1 --> (-ve) + 1 --> Can be -ve or ve depending on value of k.

E. k - 1 --> (-ve) - 1 --> -ve - 1 --> always -ve.

Option E is the correct answer.

Regards!

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Mon May 14, 2018 11:16 am

Hi alanforde800Maximus,

We're told that K is NEGATIVE. We're asked which of the following MUST also be NEGATIVE. This question can be solved by TESTing VALUES.

IF... K = -1

Answer A = (1)^2 = 1
Answer B = (-1)(-1) = 1
Answer C = 1 - (-1) = 2
Answer D = (-1) + 1 = 0
Answer E = (-1) - 1 = - 2

Final Answer: E

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

hi

by Jeff@TargetTestPrep » Tue May 15, 2018 3:43 pm

alanforde800Maximus wrote:If k is negative, which of the following must also be negative?

A) (-k)^2

B) (-1) k

C) 1 - k

D) k + 1

E) k - 1

Since 1 less than a negative number will always be negative, k - 1, will always be negative.

Answer: E

Jeffrey Miller
Head of GMAT Instruction
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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