An urn contains three red and two white balls. A ball is drawn, and then it and another ball of the same color are placed back in the urn. Finally, a second ball is drawn. a. What is the probability that the second ball drawn is white? b. if the second ball drawn is white, what is the probability that the first ball drawn was red?

A First Course in Probability (10th Edition)
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ISBN:9780134753119
Author:Sheldon Ross
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Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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My questions is about b.

 

I am confused why drawing a white ball second even affects the probability of drawing a red ball first at all. 

Intuitively I think it is independent of the second draw and therefore the answer would be 2/5 no matter what the second draw is. 

 

Help me understand? Thanks. 

An urn contains three red and two white balls. A ball is drawn,
and then it and another ball of the same color are placed back in
the urn. Finally, a second ball is drawn.
a. What is the probability that the second ball drawn is
white?
b. if the second ball drawn is white, what is the probability
that the first ball drawn was red?
Transcribed Image Text:An urn contains three red and two white balls. A ball is drawn, and then it and another ball of the same color are placed back in the urn. Finally, a second ball is drawn. a. What is the probability that the second ball drawn is white? b. if the second ball drawn is white, what is the probability that the first ball drawn was red?
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