As I have not read probability during my college, so I am not used to the formulae. I just do it conceptually & if dont find any way, I just make a guess & move forward. Here was my take.

Just consider this formation. I imagined that there are two red balls & nine white balls in a bag. I have to pick 3 balls such that not a single is red amongst them.

Red-Red-White-White-White-White-White-White-White-White-White

Probabilty of choosing white balls & not a single red ball will be:

\(\frac{9}{11} * \frac{8}{10} * \frac{7}{9} = \frac{28}{55}\)

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