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CSE21 FA11
Homework #7
(11/7/11)
7.1.
A bin contains 4 red balls, 5 white balls and 6 blue balls. A random
subset S of 4 balls is removed (without replacement). Consider the following
3 events:
(1)
E
1
: S has exactly 2 red balls.;
(2)
E
2
: S has balls of all three colors;
(3)
E
3
: S has at least 2 blue balls.
Which of the pairs of events
E
1
,E
2
and
E
3
(if any) are independent? (Justify
your answer.)
7.2.
We are given an urn that has one red ball and two white balls in it. A
fair die is thrown. If the number shown is 1 or 2 then one red ball is added
to the urn. Otherwise three red balls are added to the urn. A ball is then
randomly drawn from the urn.
(a) Given that a red ball was drawn, what is the probability that a 1 or 2
appeared when the die was thrown?
(b) Given that the ﬁnal composition of the urn contained more than one red
ball, what is the probability that a 1 or 2 appeared when the die was thrown?
7.3.
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 Fall '07
 Graham

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