A bag contains 5 white and 3 black balls. Four balls are successively drawn out without replacement. What is the probability that they are alternately of different colours?

Explanation

Probability of getting alternating colours when the firat ball is white =`5/8​xx 3/7​xx4/6​xx2/5​=1/14`
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Probability of getting alternating colours when the first ball is black=`3/8​xx5/7​xx2/6​xx4/5​=1/14`
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Probability of getting balls of alternating colour =`1/14​+1/14​=1/7`​