A Coin Is Tossed 4 Times

A coin is tossed 4 times.
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Give your answers in fraction form.
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What is the probability that the coin will land heads at least twice?
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What is the probability that the coin will land heads on the third toss given that heads were thrown on the first toss?
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What is the probability that the coin will land heads on the fourth toss given that tails were thrown on the first toss?
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