Shade from the past
I am an aspiring and successful magic user, but my math skills are, er, in need of work.
I encounter a word problem: "You toss a fair coin twice. What are the chances of getting at least one head?" Totally bollixed, I summon the shade of one of history's greatest mathematicians, Jean le Rond D'Alembert.
"There are three cases," the great D'Alembert intones. "You can get a head on the first throw. Or you can get a head on the second throw. Or you can not get a head at all. In two of those cases you get a head. So your answer is 2/3."
What is the correct answer?
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1 solution
There are actually FOUR equally probable cases.
1) head, head 2) head, tail 3) tail, head 4) tail, tail
In three of those cases there are at least one head, so the answer is 3/4.