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

 It is currently 04 Jul 2015, 06:06

### 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 Q

Author Message
TAGS:
Manager
Joined: 25 Jul 2006
Posts: 97
Followers: 1

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

probability Q [#permalink]  16 Apr 2007, 22:27
This is a repost of a Challenge question (Challenge 3, Q 26) posted several weeks back for which I have no response so far.

Store with 10 bottles of alcohol, of which 7 whiskeys.
If 6 bottles are sold, what is the prob of selling 4 whiskeys among the 6?

Given solution:
(7C4)(3C2)/(10C6) = 1/2

It seems to me that this solution assumes that 4 and only 4 whiskeys are sold. But the question doesn't exactly say that. The way the question is worded, it doesn't specify that the other 2 bottles that are sold are not whiskeys. Hence, it seems to me that we should calculate probability that atleast 4 whiskeys are sold. This gives (7C4)(6C2)/(10C6) = 5/8 as the answer (bcoz there are 6 (not 3) choices from which to pick the remaining two). Is this correct? If not, how to solve?

I am not a probability guru and would appreciate the opinion of a subject expert - since I am a little confused by this question/answer and am not sure if am on the right track.,. thanks!
Senior Manager
Joined: 01 Jan 2007
Posts: 326
Followers: 1

Kudos [?]: 19 [0], given: 0

Re: probability Q [#permalink]  17 Apr 2007, 01:17
oops wrote:
This is a repost of a Challenge question (Challenge 3, Q 26) posted several weeks back for which I have no response so far.

Store with 10 bottles of alcohol, of which 7 whiskeys.
If 6 bottles are sold, what is the prob of selling 4 whiskeys among the 6?

Given solution:
(7C4)(3C2)/(10C6) = 1/2

It seems to me that this solution assumes that 4 and only 4 whiskeys are sold. But the question doesn't exactly say that. The way the question is worded, it doesn't specify that the other 2 bottles that are sold are not whiskeys. Hence, it seems to me that we should calculate probability that atleast 4 whiskeys are sold. This gives (7C4)(6C2)/(10C6) = 5/8 as the answer (bcoz there are 6 (not 3) choices from which to pick the remaining two). Is this correct? If not, how to solve?

I am not a probability guru and would appreciate the opinion of a subject expert - since I am a little confused by this question/answer and am not sure if am on the right track.,. thanks!

Well your method is correct when the question stem says that there should be atlease 4 whiskey bottels among the bottels that are sold. well the question stem very specifically mentions that there should be 4 bottels of whiskeys and hence the given solution is correct. I am not a probability guru as well but I hope this will help.

Javed.

Cheers!
Director
Joined: 13 Mar 2007
Posts: 545
Schools: MIT Sloan
Followers: 4

Kudos [?]: 28 [0], given: 0

well, even by going with the assumption of 'atleast' 4 bottles of whiskey.

Should'nt this be the way it needs to be solved ?

p(4W) + p(5w) + p(6w) ?

=> 7c4.3c2/10c6 + 7c5.3c1/10c6 + 7c6/10c6 ?
Manager
Joined: 28 Feb 2007
Posts: 197
Location: California
Followers: 2

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

Re: probability Q [#permalink]  22 Apr 2007, 11:44
oops wrote:
This is a repost of a Challenge question (Challenge 3, Q 26) posted several weeks back for which I have no response so far.

Store with 10 bottles of alcohol, of which 7 whiskeys.
If 6 bottles are sold, what is the prob of selling 4 whiskeys among the 6?

Given solution:
(7C4)(3C2)/(10C6) = 1/2

It seems to me that this solution assumes that 4 and only 4 whiskeys are sold. But the question doesn't exactly say that. The way the question is worded, it doesn't specify that the other 2 bottles that are sold are not whiskeys. Hence, it seems to me that we should calculate probability that atleast 4 whiskeys are sold. This gives (7C4)(6C2)/(10C6) = 5/8 as the answer (bcoz there are 6 (not 3) choices from which to pick the remaining two). Is this correct? If not, how to solve?

I am not a probability guru and would appreciate the opinion of a subject expert - since I am a little confused by this question/answer and am not sure if am on the right track.,. thanks!

Probability questions are very specific on at least, at most etc. Question specifies that 4 whiskey bottles were sold. since there is no at least I would go with the given explanation. My 2 cents. (Btw, I took probability in both undergrad and grad school so I can say that i have seen reasonably good number of P questions)

hth.
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5068
Location: Singapore
Followers: 23

Kudos [?]: 194 [0], given: 0

Number of ways of picking 6 bottles from 10 = 10C6 = 210
Number of ways of picking 4 bottles of whiskey from 7 = 7C4.
Number of ways of picking 2 other bottles of alcohol = 3C2

So P = (3C2 * 7C4)/10C6
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5068
Location: Singapore
Followers: 23

Kudos [?]: 194 [0], given: 0

the question says 4 whiskeys are sold. It does not assume only 4 are sold because the question clearly states that (only 4 are sold).

If it meant anything else, it would state with phrases like 'at least'.
Manager
Joined: 25 Jul 2006
Posts: 97
Followers: 1

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

ywilfred wrote:
the question says 4 whiskeys are sold. It does not assume only 4 are sold because the question clearly states that (only 4 are sold).

If it meant anything else, it would state with phrases like 'at least'.

question doesn't say "only" - hence the confusion.
but you may be right in that if it means "atleast" or something else, it'll be specified.

this confusion originally came from a set theory question where if it doesn't say "18% watch exactly 2" or "only 2" in the below problem, the answer would be different - hence, i try to look for "only" or "exactly" to be clearly specified in the question.
http://www.gmatclub.com/phpbb/viewtopic ... rmontville
Similar topics Replies Last post
Similar
Topics:
33 In how many different ways can the letters A, A, B 22 24 Dec 2009, 15:17
Probability Q 4 15 Oct 2007, 11:32
GmatPrep -Probability Q 4 27 Sep 2006, 10:48
probability 4 08 Dec 2005, 05:14
Probability 8 19 Aug 2005, 11:12
Display posts from previous: Sort by