Question 1182471: Suppose that an urn contains three red balls marked 1, 2, 3, one blue ball marked 4, and four white balls marked 5, 6, 7, 8.
A ball is selected at random and its color and number noted.
(i) What is the probability that it is red?
(ii) What is the probability that it has an even number marked on it?
(iii) What is the probability that it is red, if it is known that the ball selected has an even number marked on it?
(iv) What is the probability that it has an even number marked on it, if it is known that the ball selected is red?
Answer by greenestamps(13208)   (Show Source):
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For (i) and (ii), use the basic definition of probability: number of favorable outcomes divided by total number of possible outcomes.
(i) (# of red)/(total number)
(ii) (# of even)/(total number)
For (iii) and (iv), use the basic definition of probability, along with the definition of conditional probability: probability of A given B is P(A and B) divided by P(B).
(iii) (# of even and red)/(# of even)
(iv) (# of even and red)/(# of red)
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