MA Economics Entrance Coaching › Forums › Subject forums › Probability & Statistics › probability
This topic contains 7 replies, has 3 voices, and was last updated by shruti290 6 years, 1 month ago.

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August 9, 2014 at 8:14 pm #498

August 10, 2014 at 7:59 am #507
take three events
A={NO RED BALL}
B={NO BLUE BALL}
C={NO WHITE BALL}
SO WE NEED TO FIND P{AUBUC}=?SO P(A)=30C10/90C10 P(B) AND P(C) WILL BE SAME
NOW P(A∩B)=60C10/90C10 P(B∩c) and p(A∩C) WIL BE SAMENOW P(A∩B∩C)=0 {CANT HAPPEN}
SO P(AUBUC}=3*{30C1060C10}/90C10
rohit pandeyQuote
August 10, 2014 at 11:05 am #508
but where is the case where 2 colors will be missing?
what i thought was tht first there are 90c10 ways in total now
case1draw 10 balls from the 30 red and 30 white balls tht means 60c10
cse 2 10 balls drawn frm 30 white and 30 blue balls tht means 60c10
case310 balls frm 30 red and 30 blue tht emans 60c10
now in all these 3 cases will also involve the cases where only red ,blue or white balss are drawn therefore to avoid double counting we subtract 3*30c10
threfore my answer becomes
3(60c1030c10)/90c10
shruti290Quote


August 10, 2014 at 11:57 am #515
just one correction p(a)=60c10/90c10
and p(a∩b)=30c10/90c10so p(aubuc)=3*{60C1030C10}/90C10
sorry had misplaced the values as i was sleepy
and p(aubuc) covers the possibility of two balls not being selected.
rohit pandeyQuote 
August 11, 2014 at 11:38 am #522

August 11, 2014 at 12:03 pm #523
my final answer aslo comes out to be the same. can anyone tell me what is my mistake?
shruti290Quote
August 11, 2014 at 3:25 pm #530
Shruti, you have only considered the case where exactly one colour is excluded. You haven’t accounted for the case where 2 colours are excluded
adminQuote
August 11, 2014 at 4:15 pm #532
But sir what i have done is tht first when i said tht we draw 10 balls frm 30 white and 30 blue balls so this sample will automatically include the case where either only 10 white balls are drwan or10 blue balls are drwan .so this does not becomes the case of exactly one color missing
shruti290Quote




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