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

 It is currently 20 Dec 2014, 07:01

### 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

# of the students at a certain school, 50% of the students are

Author Message
TAGS:
VP
Joined: 30 Sep 2004
Posts: 1490
Location: Germany
Followers: 4

Kudos [?]: 60 [0], given: 0

of the students at a certain school, 50% of the students are [#permalink]  15 Mar 2005, 07:15
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
of the students at a certain school, 50% of the students are in class a, 30% of the students are in class b, 20% of the students are in class c. of the students in class a, 20% are wearing eyeglasses. of the students in class b, 10% are wearing eyeglasses. of the students c, 10% are wearing eyeglasses. if a student is selected at random, what is the probability that the student is in class b ?
VP
Joined: 13 Jun 2004
Posts: 1123
Location: London, UK
Schools: Tuck'08
Followers: 6

Kudos [?]: 26 [0], given: 0

I think the question is not complete...because the glasses story is totally useless so I assume that normally it should be a question in realtion with the prob of someone from class b with glasses or without glasses...

maybe I've missed something

if not, my answer is 3/10
Manager
Joined: 17 Dec 2004
Posts: 73
Followers: 2

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

If 30% of the students are in class B, the probability of one of them being picked is clearly 3/10. Is part of the question missing?
VP
Joined: 13 Jun 2004
Posts: 1123
Location: London, UK
Schools: Tuck'08
Followers: 6

Kudos [?]: 26 [0], given: 0

christoph please explain or check again your question because I don't get it... please explain the way of thinking
VP
Joined: 30 Sep 2004
Posts: 1490
Location: Germany
Followers: 4

Kudos [?]: 60 [0], given: 0

Antmavel wrote:
christoph please explain or check again your question because I don't get it... please explain the way of thinking

possible outcomes: 30% of the students are in class b * of the students in class b, 10% are wearing eyeglasses = 0,1 * 0,3 = 0,03

all outcomes: 50% of the students are in class a * of the students in class a 20% are wearing eyeglasses + 30% of the students are in class b * of the students in class b, 10% are wearing eyeglasses + 20% of the students are in class c * of the students c, 10% are wearing eyeglasses = 0,15

is it clear ?
VP
Joined: 13 Jun 2004
Posts: 1123
Location: London, UK
Schools: Tuck'08
Followers: 6

Kudos [?]: 26 [0], given: 0

Re: PS - Bayes Theorem [#permalink]  21 Mar 2005, 02:56
christoph wrote:
if a student is selected at random, what is the probability that the student is in class b ?

I think there is a mistake in the first post. Actually the answer to this question should be :
total outcome : all students
favorable outcome : all students in class b

however, the solution you've given us is
total outcome : all students with glasses
favorable outcome : all students with glasses in class b

Is it clear ?
Senior Manager
Joined: 19 Nov 2004
Posts: 284
Location: Germany
Followers: 1

Kudos [?]: 11 [0], given: 0

Christoph, I still don't get it.

The question asks "what is the probability that the student is in class b": How can the possible outcomes depend on the number of students wearing glasses or not?

Is there something missing in the question or something which I have misinterpreted?

Thanks.
VP
Joined: 30 Sep 2004
Posts: 1490
Location: Germany
Followers: 4

Kudos [?]: 60 [0], given: 0

hm? you guys are right. i think the question is wrong. it should be: "what is the probability that the student in class b is wearing glasses?" sorry !
Manager
Joined: 11 Jan 2005
Posts: 57
Location: Mexico City
Followers: 1

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

It would be 30%*10%= 3%

Another interesting way to look at it would be what percent of students do not wear eyeglasses.

(50%*20%)+(30%*10%)+(20%*10%)= 10%+3%+2%= 15%
Similar topics Replies Last post
Similar
Topics:
At least 100 students at a certain high school study 1 25 Oct 2005, 23:21
Of the students at a certain school, 30% of the students are 2 07 Oct 2005, 08:11
Of the students at a certain business school, 60% are 10 03 Oct 2005, 06:04
of the students at a certain school, 50% of the students are 6 15 Mar 2005, 07:13
The mean weight of 500 male students at a certain school is 9 10 Feb 2005, 08:53
Display posts from previous: Sort by