It is currently 20 Jan 2018, 16:58

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If a number is to be randomly selected from set A above and a number

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Expert Post
1 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 43334

Kudos [?]: 139605 [1], given: 12794

If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 00:49
1
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

55% (01:18) correct 45% (01:15) wrong based on 42 sessions

HideShow timer Statistics

GMAT CLUB'S FRESH CHALLENGE QUESTION:



A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 21/49
[Reveal] Spoiler: OA

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 139605 [1], given: 12794

Intern
Intern
avatar
B
Joined: 05 Mar 2015
Posts: 14

Kudos [?]: 1 [0], given: 33

Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 02:49
I think answer is A

There are 7x7=49 possible products

And 8 oh them yield negative integers

1) -10x1/5
2) -10x1/2
3) -9x1/3
4) -8x1/2
5) -6x1/3
6) -6x1/2
7) -5x1/5
8) -4x1/2

Kudos [?]: 1 [0], given: 33

Intern
Intern
avatar
B
Joined: 02 Mar 2017
Posts: 9

Kudos [?]: 0 [0], given: 16

Premium Member
Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 04:08
A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 24/49
--------------
Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7
For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem

Kudos [?]: 0 [0], given: 16

Intern
Intern
avatar
B
Joined: 05 Mar 2015
Posts: 14

Kudos [?]: 1 [0], given: 33

Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 04:25
Munch wrote:
A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 24/49
--------------
Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7
For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem



]The question specifically asks for integers,

Kudos [?]: 1 [0], given: 33

Intern
Intern
avatar
B
Joined: 02 Mar 2017
Posts: 9

Kudos [?]: 0 [0], given: 16

Premium Member
Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 04:30
kablayi wrote:
Munch wrote:
A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 24/49
--------------
Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7
For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem



]The question specifically asks for integers,


Oh ya!! thanks!! then it should be 8 .. I doubled checked the possibility to match the answer, but still missed the word integer..

Kudos [?]: 0 [0], given: 16

Manager
Manager
User avatar
B
Joined: 05 Oct 2014
Posts: 64

Kudos [?]: 13 [0], given: 162

Location: India
Concentration: General Management, Strategy
GMAT 1: 580 Q41 V28
GPA: 3.8
WE: Project Management (Energy and Utilities)
Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 05:28
A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

I am not sure whether we should consider the product numbers of ‘0’.

Considering ‘0’ as an eligible possibility,
A X B will be -ve when, either A or B is -ve. Since all values for A is -ve, then all values of B must be +ve. In such case, only pairs will be -ve when value of B is 1/5 , 1/3 or 1/2.
For each A, there will be 3 Negative Values, i.e
A X B = -10*1/5 = -10/5 ; -10/3 ; -10/2
= -9/5 ; -9/3 ; -9/2
.
.
.
and so on.

Thus possible negative values will be = 7*3 =21

Total Possible product values will be = 7*7=49

Thus P(E) = 21/49. Option E is right.

Kudos [?]: 13 [0], given: 162

1 KUDOS received
Intern
Intern
avatar
B
Joined: 29 Sep 2017
Posts: 1

Kudos [?]: 1 [1], given: 2

CAT Tests
Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 06:04
1
This post received
KUDOS
The question specifically asks for -ve integers("0" is not a -ve integer). Now Set A has only -ve integers so we have to select only +ve fractions from set B i.e.{1/5,1/3,1/2}.
With 1/5 we can only select -10 & -5 from set A. So possible combinations : 1/5*-10 & 1/5*-5. Number of possible combinations = 2

With 1/3 we can only select -9 & -6 from set A. Number of possible combinations = 2
With 1/2 we can only select -10,-8,-6,-4 from set A. Number of possible combinations = 4
Thus we have 2+2+4 = 8 combinations
Total Possible combinations = 7C1 * 7C1 = 49
Ans = 8/49

Kudos [?]: 1 [1], given: 2

Expert Post
Math Expert
User avatar
D
Joined: 02 Aug 2009
Posts: 5536

Kudos [?]: 6441 [0], given: 122

Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 16:57
Bunuel wrote:

GMAT CLUB'S FRESH CHALLENGE QUESTION:



A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 21/49



Since we are looking for negative integer, we have to consider only POSITIVE numbers in set B as all are NEGATIVE in set A..
1) 1/2
This will give integers when multiplied by MULTIPLE of 2
So -4,-6,-8,-10......4ways
2) 1/3
Similarly when multiplied by MULTIPLE of 3
-6,-9.....2ways
3) 1/5
When multiplied by MULTIPLE of 5
So -5,-10.....2ways

Total - 4+2+2=8ways
Possible products = 7*7=49

Ans 8/49

A
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html


BANGALORE/-

Kudos [?]: 6441 [0], given: 122

Manager
Manager
User avatar
B
Joined: 05 Oct 2014
Posts: 64

Kudos [?]: 13 [0], given: 162

Location: India
Concentration: General Management, Strategy
GMAT 1: 580 Q41 V28
GPA: 3.8
WE: Project Management (Energy and Utilities)
Re: If a number is to be randomly selected from set A above and a number [#permalink]

Show Tags

New post 13 Dec 2017, 18:59
chetan2u wrote:
Bunuel wrote:

GMAT CLUB'S FRESH CHALLENGE QUESTION:



A = {-10, -9, -8, -7, -6, -5, -4}
B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49
B. 12/49
C. 13/49
D. 18/49
E. 21/49


I missed the INTEGER PART :cry:

Since we are looking for negative integer, we have to consider only POSITIVE numbers in set B as all are NEGATIVE in set A..
1) 1/2
This will give integers when multiplied by MULTIPLE of 2
So -4,-6,-8,-10......4ways
2) 1/3
Similarly when multiplied by MULTIPLE of 3
-6,-9.....2ways
3) 1/5
When multiplied by MULTIPLE of 5
So -5,-10.....2ways

Total - 4+2+2=8ways
Possible products = 7*7=49

Ans 8/49

A

Kudos [?]: 13 [0], given: 162

Re: If a number is to be randomly selected from set A above and a number   [#permalink] 13 Dec 2017, 18:59
Display posts from previous: Sort by

If a number is to be randomly selected from set A above and a number

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.