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

 It is currently 16 Jan 2019, 11:12

### 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 January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
• ### The winning strategy for a high GRE score

January 17, 2019

January 17, 2019

08:00 AM PST

09:00 AM PST

Learn the winning strategy for a high GRE score — what do people who reach a high score do differently? We're going to share insights, tips and strategies from data we've collected from over 50,000 students who used examPAL.
• ### Free GMAT Strategy Webinar

January 19, 2019

January 19, 2019

07:00 AM PST

09:00 AM PST

Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

# Probabilities Question

Author Message
Intern
Joined: 15 Sep 2005
Posts: 13
Location: London

### Show Tags

15 Sep 2005, 12:15
1
Hi again, I got another question, this time about probabilities:

There are 10 different stamps. Peter's collection includes 3 stamps of the 10. If 2 stamps are drawn from the 10, what is the probability that neither of the 2 stamps are among the 3 held by Peter?

Thanks!

M

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
VP
Joined: 22 Aug 2005
Posts: 1073
Location: CA

### Show Tags

Updated on: 15 Sep 2005, 13:51
Lets first find probability when BOTH two stamps drawn are from the Peter's collection of 3 stamps. The probability for this would be:

3C2 / 10C2 = 3/45 = 1/15

Probability that ONE of the stamp picked matched that of Peter's collection =

3C1 / 10C2 = 3/45 = 1/15

the probability that NIETHER was from Peter's collection = 1 - 1/15 - 1/15 or
p = 13/15

Originally posted by duttsit on 15 Sep 2005, 12:29.
Last edited by duttsit on 15 Sep 2005, 13:51, edited 1 time in total.
Senior Manager
Joined: 29 Nov 2004
Posts: 443
Location: Chicago

### Show Tags

15 Sep 2005, 13:00
7/10*6/9 = 7/15
_________________

Fear Mediocrity, Respect Ignorance

VP
Joined: 22 Aug 2005
Posts: 1073
Location: CA

### Show Tags

Updated on: 15 Sep 2005, 14:00
ranga41 wrote:
7/10*6/9 = 7/15

hows the second draw probability 6/9 here? wont it depend on first draw. I mean if:
A) first draw resulted into one of the stamp in peter's collection, this probability would be : 7/9

B) first draw did not result into perter's collection stamps, second draw probability would be:
6/9

As first draw probability remains same, the total probability would be:

7/10 * 7/9 + 7/10 * 6/9 or 91/90

Guess ans to this question depends/changes on if:
- both stamps are drawn "together"
- stamps are drawn one after another.

The ans will vary based on the two.

Originally posted by duttsit on 15 Sep 2005, 13:33.
Last edited by duttsit on 15 Sep 2005, 14:00, edited 2 times in total.
Intern
Joined: 05 May 2005
Posts: 40

### Show Tags

15 Sep 2005, 13:35
First pick: 7/10 stamps are NOT included in Peter's collection
Second pick: 6/9 stamps are NOT included in Peter's collection, since there are 9 stamps left and 3 of those 9 are within his collection

7/10 * 6/9 = 7/15
Intern
Joined: 14 Jun 2005
Posts: 37

### Show Tags

15 Sep 2005, 21:21
Can we use binomial distribution here ?????

10C2*(7/10)^2*(3/10)^8
Intern
Joined: 09 Sep 2005
Posts: 17

### Show Tags

16 Sep 2005, 05:50
You draw first time and it is 7/10 to miss
Then you draw second time and it 6/9 to miss
So - 6*7/90
Manager
Joined: 06 Aug 2005
Posts: 193

### Show Tags

20 Sep 2005, 04:41
silentell wrote:
First pick: 7/10 stamps are NOT included in Peter's collection
Second pick: 6/9 stamps are NOT included in Peter's collection, since there are 9 stamps left and 3 of those 9 are within his collection

7/10 * 6/9 = 7/15

7/15 looks good to me.

I think that the suggestion of 91/90 is improbable, indeed impossible !

0<= P <= 1 for all probabilities.
Intern
Joined: 16 Aug 2005
Posts: 23
Location: India

### Show Tags

20 Sep 2005, 05:47
don't overthink it. It is as simple as 7c2/10c2= 7/15

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Non-Human User
Joined: 09 Sep 2013
Posts: 9415

### Show Tags

20 Dec 2018, 19:12
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: Probabilities Question &nbs [#permalink] 20 Dec 2018, 19:12
Display posts from previous: Sort by