There are...

Question

There are 4 red, 4 white, and 4 blue marbles in an urn. Two marbles are selected at random without replacement. What is the probability that neither is red, given that neither is white?

Answer 1

Let R'=event neither is RED, W'=event neither is WHITE

 

(1) P(R'|W') = P(R'W')/P(W')

 

 

the numerator on the right says the same thing as both are BLUE (not Red nor White)

 

(2) this gives P(R'W')=(4/12)(3/11)    that is first blue; then 2nd blue

 

 

(3) The denominator says neither is W.  so P(W')= (       ) (        )  can you fill this one in?

 

If so put the answers from lines (2) and (3) on the right side in line (1) to get the final answer.

 

 

Of course if you need more steps let me know.

 

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