There are 6 white and 4 black balls in a bag. If four are drawn successively (and not replaced),find the probability that they are alternately of different colour.

Explanation

There are 6 white and 4 black balls in a bag. Four balls are drawn without replacement. Let W and B denotes the white and black ball. There are two mutually exclusive cases WBWB and BWBW.
`therefore P(WBWB)=6/10xx4/9xx5/8xx3/7=1/14`
P(BWBW)=`4/10xx6/9xx3/8xx5/7xx=1/14`
`therefore` Probability that they are alternately of different colour`=1/14+1/14=2/14=1/7`