I'm suck at Probability, so I need your help on this

let says each chocolate bar contains a card chosen out of $K$ different types with equal probability. A jackpot is offered when r different types of cards are obtained ($K\geqslant r$). I would like to know how to find the probability of obtaining cards of $r$ different types for the first time after buying $n$ bars.

Thanks in advance

  • $\begingroup$ Thank you Jose Carlos Santos for editing my question $\endgroup$ – KEI Jul 26 '17 at 9:05
  • $\begingroup$ Does 'for the first time' means that there were only $r-1$ different types of cards among the $n-1$ first bars, and you found a $r$-th type of cards in the $n$-th bar ? $\endgroup$ – Evargalo Jul 26 '17 at 12:31
  • $\begingroup$ @Evargalo I think there were still r different types of cards among n bars but for the first time maybe implies the probability of trials before success $\endgroup$ – KEI Jul 26 '17 at 15:17

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