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SVP
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of the students at a certain school, 50% of the students are [#permalink]
 15 Mar 2005, 08:13
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 wearing eyeglasses ?
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GMAT Club Legend
Joined: 07 Jul 2004
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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.
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Intern
Joined: 17 Feb 2005
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Location: SE Michigan
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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
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GMAT Club Legend
Joined: 07 Jul 2004
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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.
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Senior Manager
Joined: 15 Feb 2005
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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
answer=3/20
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SVP
Joined: 30 Sep 2004
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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
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Manager
Joined: 17 Dec 2004
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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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