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Box- 6 red and 2 white

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by MURALIDHARGAJULA » Thu Jun 02, 2011 11:55 pm
A box contains 6 red and 2 white balls. Alice, Jane and Kate keep on drawing a ball in succession till a white ball is drawn. What is the probability that Jane draws white ball?

A) 3/14
B) 3/28
C) 15/28
D) 3/10
E) 9/28

OA E
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by cans » Fri Jun 03, 2011 12:13 am
A,J,K draw white ball in succession.
P(J draws)=p(RW) + p(rrrrw)= (6/8)*(2/7) + (6/8)(5/7)(4/6)(3/5)(2/4) = 3/14 + 3/28 = 9/28
IMO E
RW - Alice draws red, Jane draws white and game stops
rrrw, alice draws red, jane misses white and draws red, kate draws red, and den again alice draws red and this time jane draws white.
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by Ozlemg » Fri Jun 03, 2011 12:51 am
Hi Cans,
Thank you for your explanation indeed.
I got the logic, no problem in there but I have a question :

P(J draws)=p(RW) + p(rrrrw)= (6/8)*(2/7) + (6/8)(5/7)(4/6)(3/5)(2/4) = 3/14 + 3/28 = 9/28

The fraction I colored red is the probability of drawing white out of 2 white balls. Isn't it?
It is not the descending probability of drawing red?
The more you suffer before the test, the less you will do so in the test! :)
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by cans » Fri Jun 03, 2011 3:24 am
Ozlemg wrote:Hi Cans,
Thank you for your explanation indeed.
I got the logic, no problem in there but I have a question :

P(J draws)=p(RW) + p(rrrrw)= (6/8)*(2/7) + (6/8)(5/7)(4/6)(3/5)(2/4) = 3/14 + 3/28 = 9/28

The fraction I colored red is the probability of drawing white out of 2 white balls. Isn't it?
It is not the descending probability of drawing red?
Yup it is probability of selecting a white ball out of remaining 4 balls :)
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by vikram4689 » Fri Jun 03, 2011 7:38 am
Why the last case is not considered. According to me there are 3 cases

RW = 3/14
RRRRW = 3/28
RRRRRRRW = 1/28
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by galaxian » Fri Jun 03, 2011 11:53 pm
We have only 6 Red Balls & hence no last case.
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by smackmartine » Sat Jun 04, 2011 12:10 am
cans wrote:A,J,K draw white ball in succession.
P(J draws)=p(RW) + p(rrrrw)= (6/8)*(2/7) + (6/8)(5/7)(4/6)(3/5)(2/4) = 3/14 + 3/28 = 9/28
IMO E
RW - Alice draws red, Jane draws white and game stops
rrrw, alice draws red, jane misses white and draws red, kate draws red, and den again alice draws red and this time jane draws white.
I am waiting to hear your quants score :)
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by cans » Sat Jun 04, 2011 8:49 am
smackmartine wrote:
cans wrote:A,J,K draw white ball in succession.
P(J draws)=p(RW) + p(rrrrw)= (6/8)*(2/7) + (6/8)(5/7)(4/6)(3/5)(2/4) = 3/14 + 3/28 = 9/28
IMO E
RW - Alice draws red, Jane draws white and game stops
rrrw, alice draws red, jane misses white and draws red, kate draws red, and den again alice draws red and this time jane draws white.
I am waiting to hear your quants score :)
Thanks smackmartine :) It feels so good to hear nice compliments like this :)
If my post helped you- let me know by pushing the thanks button ;)

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Cans!!
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by sandeep800 » Sun Jun 05, 2011 10:45 am
U r great in Quant Cans :) Thanx
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