Bunuel wrote:
A pyramid of 12 playing cards is such a state that if any individual card falls, the entire pyramid collapses. If for each individual card, the probability of falling during time period of 1 minute is 0.05, what is the probability that the pyramid will collapse during time period of 1 minute?
(A) 0.05
(B) 0.05^12
(C) 1 − 0.95^12
(D) 0.95^12
(E) 1 − 0.05^12
Since the probability that a card will fall is 0.05, we see that the probability that a card will NOT fall is 1 - 0.05 = 0.95.
This question is asking the probability that the pyramid collapses (i.e., that at least one card falls) in the 1-minute time period..We can use the formula 1 - P(no card falls) = P(at least one card falls).
P(no card falls) = 0.95^12, so P(at least one card falls) is 1 - 0.95^12.
Answer: C
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55% (01:23) correct 
