题目内容：

sat2
A two-sided coin is flipped four times.Given that the coin landed heads up more than twice,what is the probability that it landed heads up all four times?
答案是1/5
why

优质解答

Well, since it has been flipped four times, and more than twice with heads up (which is, at least 3 times), only the last time counts.
It is very obvious that the last time will see this two-sided coin either landed heads up or tails up, and the probability is 50%.
So the answer is 50%.