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antoni7
In a bag there are 2 black and 4 white identical rings. Two rings are drawn from the bag at random. Find the probability that only one of them is white.
first one is black AND second one is white OR first one is white AND second one is black is one way to proceed
\[\frac{2}{6}\times \frac{4}{5}+\frac{4}{6}\times \frac{1}{5}\] is one way there are others
for example you could compute \[\frac{\binom{4}{1}\times \binom{2}{1}}{\binom{6}{2}}\]
second way is probably snappier, gives \[\frac{8}{15}\] right away
@satellite73 May be there is a mistake in your second post? Can you please explain why does the second way give the right result?