Laura buys an unfair coin online. The coin is supposed to land heads up 75% of the time. If this is true, what is the probability that in 20 flips, the first 15 land heads up and the last 5 land tails up?

For this exact sequence, multiply the probability of each flip: 15 heads each have probability 0.75, and 5 tails each have probability 0.25. Thus the probability is (0.75)^15(0.25)^5, which is choice C. The order is specified, so there is no need to multiply by the number of possible arrangements.

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