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The sample space when flipping a coin is [heads, tails].
fraction for flipping one coin one time = 1/2
The probability of flipping Heads on a coin is 1 - a certainty - if the coin is flipped often enough.
On a single toss of a fair coin the probability is 1/2.
For a normal coin, it is 0.5.
There are 8 permutations of flipping a coin 3 times, or of flipping 3 coins one time. They are, with the permutations of two heads bolded...
TTT
TTH
THT
THH
HTT
HTH
HHT
HHH
... thus, the probability of flipping a coin 3 times and getting 2 heads is 3 in 8, or 0.375.