1) Given that we have already tossed a balanced coin ten times and obtained zero heads, what is the probability that we must tossed it at least two more times to obtain the first head?

hyper geometric probability

Twenty identical looking packets of white powder such that 15 contain cocaine and 5 do not. 4 packet randomly selected and found to contain cocaine. 2 additional were selected from remainder so sold to a person. what is the probability 6 packets randomly selected such that first 4 contain cocaine and 2 sold to the buyer do not?