Answer: 1 in 8
Step-by-step explanation: The probability of getting 3 heads when you toss a "fair" coin three times is (as others have said) 1 in 8, or 12.5%. However, that isn't the question you asked. If you toss a coin exactly three times, there are 8 equally likely outcomes, and only one of them contains 3 consecutive heads. So the probability is 1 in 8.