A bag contains blue balls and red balls. Two balls are drawn in succession without replacement. What is the probability that one ball is blue and the other is red?
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Case 1: First draw is blue and second draw is red.
P 1 = 9 5 × 8 4 = 1 8 5
Case 2: First draw is red and second draw is blue.
P 2 = 9 4 × 8 5 = 1 8 5
Thus, the probability is
P = P 1 + P 2 = 1 8 5 + 1 8 5 = 9 5