Latest RRB Aptitude Question SOLUTION: An urn contains three white and four black balls. We take out a ball and put it in a drawer without looking at it. After that we take out a second ball. Find the probability that t

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(#M40107604) RRB Category question Keep an EYE

An urn contains three white and four black balls. We take out a ball and put it in a drawer without looking at it. After that we take out a second ball. Find the probability that this ball is white.

Asked In RRB Jaspalsingh Parmar (9 years ago)

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purva  (9 years ago)

let us assume that first ball drawn is white and second ball is also white OR first ball drawn is Black and second ball drawn is White
so,
W W OR B W
probability of drawing first white ball = 3/7 as total 7 balls
probability of drawing sec. white ball=2/6
similarly probability of drawing first black ball =4/7
then white ball = 3/6
hence, total probability is
3/7*2/6 + 4/7*3/6
= 3/7
=

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bavya  (9 years ago)

Ans 5/6
(3C1+2C1)/(6C1)

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ABHISHEK  (9 years ago)

2 cases-W,W AND B,W
(3/7)*(2/6)+(4/7)*(3/6)=3/7

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YANAMALA RAMESH  (8 years ago)

2 cases-W,W AND B,W
(3/7)*(2/6)+(4/7)*(3/6)=3/7

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