My knowledge about this kind of problems is almost zero, so I need some help.(adsbygoogle = window.adsbygoogle || []).push({});

I know that if we have 20 balls in a urn, 1 to 20, the probability to extract 1 to 5 in a extraction is 5/20=1/4

But what if we have 4 extractions with the balls extracted put back in the urn? How do I calculate that ?

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# Probability to extract balls problem

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