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

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

Kudos [?]: 91 [0], given: 0

of the students at a certain school, 50% of the students are [#permalink]  15 Mar 2005, 07:13
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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 wearing eyeglasses ?
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5078
Location: Singapore
Followers: 22

Kudos [?]: 184 [0], given: 0

I got 9/50.

My solution is in a word document as I used a table to solve the question. I can't display the table properly here. However, I also can't find a button to let me make an attachement. I don't know if I got my rights to attach files disabled or I am pure blind and can't find it
Maybe the moderators can help me with the attachement.
Intern
Joined: 17 Feb 2005
Posts: 28
Location: SE Michigan
Followers: 0

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

A:B:C
50:30:20

In A
Glasses: No Glasses
10:40

In B
Glasses: No Glasses
3:27

In C
Glasses: No Glasses
2:18

So in total,

15 wear glasses out of 100

req. probability= 15/100
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5078
Location: Singapore
Followers: 22

Kudos [?]: 184 [0], given: 0

ywilfred wrote:
I got 9/50.

My solution is in a word document as I used a table to solve the question. I can't display the table properly here. However, I also can't find a button to let me make an attachement. I don't know if I got my rights to attach files disabled or I am pure blind and can't find it
Maybe the moderators can help me with the attachement.

Made a mistake with my table. Yes, answer is 3/20 (15/100). But I'm still not able to attach my document. Can someone tell me why ?

In any case, my working is the same as amit_upasan's.
Manager
Joined: 15 Feb 2005
Posts: 247
Location: Rockville
Followers: 1

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

A:(prob of picking a student from class A)*(prob of picking a student with glasses)=2/10*1/2
do the same for a student from class B and C
B: 3/10*1/10
C: 2/10*1/10
A+B+C
VP
Joined: 30 Sep 2004
Posts: 1490
Location: Germany
Followers: 4

Kudos [?]: 91 [0], given: 0

0,5*0,2+0,3*0,1+0,2*0,1=0,15=15%

now it is easy to see the connection to the other question => http://www.gmatclub.com/phpbb/viewtopic.php?t=14826
Manager
Joined: 17 Dec 2004
Posts: 73
Followers: 2

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

I got 3/20 as well:

A - 50% students, 20% wear glasses = 10% of total students
B - 30% students, 10% wear glasses = 3% of total students
C - 20% students, 10% wear glasses = 2% of total students

which leads to 15% of total students wear glasses

15/100 = 3/20
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# of the students at a certain school, 50% of the students are

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