Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 25 Sep 2016, 14:42

### 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 June
Open Detailed Calendar

# Probability (m02q06)

Author Message
Senior Manager
Joined: 05 Oct 2008
Posts: 271
Followers: 3

Kudos [?]: 335 [0], given: 22

### Show Tags

25 Oct 2008, 21:54
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

In preparation for the Olympics, a group of five women is participating in a 400 meter race. What is the probability that either Jenny or Sally will win this race?

(A) $$\frac{1}{5}$$
(B) $$\frac{4}{15}$$
(C) $$\frac{2}{5}$$
(D) $$\frac{1}{2}$$
(E) $$\frac{3}{5}$$

[Reveal] Spoiler: OA
C

Source: GMAT Club Tests - hardest GMAT questions

When do we use the logic - A or B = P(A) + P(A) - P(A&B)
Senior Manager
Joined: 28 Feb 2007
Posts: 306
Followers: 1

Kudos [?]: 40 [3] , given: 0

### Show Tags

26 Oct 2008, 01:05
3
KUDOS
1) if the question stem supposed there is only one winner then
Probab for J is 1/5
for S is 1/5
for J or S=1/5+1/5=2/5

In order to use the formula u provided two events must overlap.
ex: There 20 students. 12 are member of Drum club. 15 are members of Soccer club. If all the students are members of either club or both.What is the probability that a rendomly chosen student is a member of either club but not both.

2) But winner(s) can be 1,2,3,4,5 at the same time, why can't they cross the finish at the sametime? If this is case then it gets way complex.
VP
Joined: 30 Jun 2008
Posts: 1043
Followers: 14

Kudos [?]: 526 [0], given: 1

### Show Tags

26 Oct 2008, 01:09
UMB wrote:
1) if the question stem supposed there is only one winner then
Probab for J is 1/5
for S is 1/5
for J or S=1/5+1/5=2/5

In order to use the formula u provided two events must overlap.
ex: There 20 students. 12 are member of Drum club. 15 are members of Soccer club. If all the students are members of either club or both.What is the probability that a rendomly chosen student is a member of either club but not both.

2) But winner(s) can be 1,2,3,4,5 at the same time, why can't they cross the finish at the sametime? If this is case then it gets way complex.

I guess we proceed with the assumption that only one completes the race first ....
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Senior Manager
Joined: 05 Oct 2008
Posts: 271
Followers: 3

Kudos [?]: 335 [0], given: 22

### Show Tags

26 Oct 2008, 06:18
Excellent explanation UMB - thanks for your time.

Kudos given.
Intern
Joined: 15 Nov 2009
Posts: 29
Schools: Kelley
Followers: 0

Kudos [?]: 8 [1] , given: 4

### Show Tags

11 Feb 2010, 07:49
1
KUDOS
Hay Why cant there be four Jennys and one Sally among the five. Or Three Sallys and Two Jennnys? Etc.

The question does not specify names of all five participants....
Manager
Joined: 26 Nov 2009
Posts: 175
Followers: 3

Kudos [?]: 56 [0], given: 5

### Show Tags

11 Feb 2010, 11:44
If the question is a DS then we can pick ans choice E as you stated but it is a problem solving type of question so we should move on... and also either Jenny or Jan clearly denotes that they are just 2 out of 5 from the group... So my choice is 2/5

Posted from my mobile device
Intern
Joined: 15 Nov 2009
Posts: 31
Location: Moscow, Russia
Followers: 0

Kudos [?]: 12 [0], given: 0

### Show Tags

11 Feb 2010, 12:11
Any of the five women may win - five outcomes, two of them suit the condition, so 2/5.
Intern
Joined: 27 Jan 2010
Posts: 4
Followers: 0

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

### Show Tags

12 Feb 2010, 01:22
nvgroshar wrote:
Any of the five women may win - five outcomes, two of them suit the condition, so 2/5.

No of ways in which either one of them can win = 2c1 = 2

No of ways in which one can win (total no. of outcomes) = 5c1 = 5

So P = 2c1/5c1 = 2/5
Manager
Joined: 10 Feb 2010
Posts: 193
Followers: 2

Kudos [?]: 94 [0], given: 6

### Show Tags

12 Feb 2010, 19:55
If only one of Jenny or Sally wins: 1/5 + 1/5 = 2/5

If (maybe) both win: 1/5 + 1/5 - 1/25 = 9/25

Only 2/5 is in the options, so we can safely go bo that!
Manager
Joined: 11 Feb 2011
Posts: 80
Followers: 1

Kudos [?]: 2 [0], given: 0

### Show Tags

16 Feb 2011, 14:23
lets say _ _ _ _ _ _ five places to fill.
First place should be either jenny or sally can be filled in two ways. Second place in 4 ways as one women place is fixed.
third place in 3 ways, and fourth in 2 & fifth in one way ==> 2* 4* 3* 2* 1
In general, if it is to fill five places with five women can be done in 5*4*3*2*1 ways

Probality is (2*4*3*2*1)/(5*4*3*2*1) = 2/5 C
Manager
Joined: 26 Sep 2010
Posts: 155
Nationality: Indian
Concentration: Entrepreneurship, General Management
GMAT 1: 760 Q V
Followers: 7

Kudos [?]: 58 [0], given: 18

### Show Tags

16 Feb 2011, 15:40
If it was a DS question , answer would be different. Here it is clearly C).

Posted from my mobile device
_________________

You have to have a darkness...for the dawn to come.

Manager
Joined: 28 Oct 2009
Posts: 92
Followers: 1

Kudos [?]: 92 [0], given: 42

### Show Tags

16 Feb 2011, 19:52
The equation; p(a) + p(b) - p(aandb) would be used if the question had asked for the probability of j or s but not both.
Manager
Joined: 04 Dec 2009
Posts: 71
Location: INDIA
Followers: 2

Kudos [?]: 9 [0], given: 4

### Show Tags

16 Feb 2011, 22:26
ans:c 1/5+1/5 =2/5

easy one
_________________

MBA (Mind , Body and Attitude )

Intern
Joined: 29 Nov 2010
Posts: 3
Followers: 0

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

### Show Tags

17 Feb 2011, 00:52
simple one: 1/5+1/5=2/5 is ans.
Current Student
Status: Up again.
Joined: 31 Oct 2010
Posts: 541
Concentration: Strategy, Operations
GMAT 1: 710 Q48 V40
GMAT 2: 740 Q49 V42
Followers: 20

Kudos [?]: 356 [0], given: 75

### Show Tags

18 Feb 2011, 07:57
Assuming only one of them can win, the probability will be 1/5 + 1/5 = 2/5.

Wow! I guess this would be one of the simpler problems of the GMAT club tests..
_________________

My GMAT debrief: http://gmatclub.com/forum/from-620-to-710-my-gmat-journey-114437.html

Manager
Joined: 02 Feb 2012
Posts: 195
Location: United States
GPA: 3.08
Followers: 1

Kudos [?]: 5 [0], given: 104

### Show Tags

20 Feb 2012, 18:00
I got C as well, was worried that there might be a trick. Apparently not!
Manager
Joined: 03 Feb 2012
Posts: 56
Location: United States (WI)
Concentration: Other
Schools: University of Wisconsin (Madison) - Class of 2014
GMAT 1: 680 Q46 V38
GMAT 2: 760 Q48 V46
GPA: 3.66
WE: Marketing (Manufacturing)
Followers: 0

Kudos [?]: 27 [0], given: 12

### Show Tags

20 Feb 2012, 19:31
When a probability questions asks "or", that's usually a signal to use A or B = P(A) + P(A) - P(A&B). When the events are mutually exclusive (only one can win a race in all but the most unlikely of outcomes) P(A&B) = 0 so you're left with A or B = P(A) + P(A).
Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 178
Location: India
WE: Information Technology (Investment Banking)
Followers: 3

Kudos [?]: 70 [0], given: 1

### Show Tags

20 Feb 2012, 23:48
Another way to solve this question.
Since either S or J has to win the race so make them as one group so now we have 4c1
and the total no of events is 5c2
so probability is 4c1/5c2 = 2/5
Intern
Joined: 19 Aug 2011
Posts: 29
Concentration: Finance, Entrepreneurship
Followers: 0

Kudos [?]: 13 [0], given: 2

### Show Tags

21 Feb 2012, 05:07
Since (A&B) = 0 in this case, hence ans is P(A) + P(B)
Intern
Joined: 15 Apr 2011
Posts: 49
Followers: 0

Kudos [?]: 5 [0], given: 8

### Show Tags

20 Feb 2013, 14:09
(1/5)+(1/5)=2/5
If it was AND situation it would be multiplication.

c

Posted from my mobile device
Re: Probability (m02q06)   [#permalink] 20 Feb 2013, 14:09

Go to page    1   2    Next  [ 22 posts ]

Similar topics Replies Last post
Similar
Topics:
Probability Question 3 06 Sep 2010, 18:50
Probability Die 2 07 Jun 2010, 00:10
1 Probability 2 22 Jan 2010, 10:30
5 Probability (m01q04) 30 06 May 2008, 04:57
Event A and Event B are independent. Is the probability that 6 23 Oct 2007, 08:13
Display posts from previous: Sort by

# Probability (m02q06)

Moderator: Bunuel

 Powered by phpBB © phpBB Group and phpBB SEO 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®.