If a box contains 4 red balls and 6 blue balls then what is the probability of picking 2 balls of the same colour?
7/15
Total number of balls = 4 + 6 = 10 Probability of picking 2 red balls = (4C2) / (10C2) = (4*3)/(10*9) = 12/90 = 2/15 Probability of picking 2 blue balls = (6C2) / (10C2) = (6*5)/(10*9) = 30/90 = 1/3 Probability of picking 2 balls of the same color = Probability of picking 2 red balls + Probability of picking 2 blue balls = 2/15 + 1/3 = 2/15 + 5/15 = 7/15
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