One Head and Three Tails will be obtained in tossing the coins only four times. If the coin is tossed five times, combination of One Head and Three Tails will not exist. To this extent the question needs to be reworded. Now Assuming that a coin is tossed four times, the following tree diagram would illustrate various combinations of Heads and Tails (total 16 in all). There will be four combination of One head and Three Tails as highlighted in red. The required probability would thus be 4 out of 16 or, 1/4 .

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