A. Since the tosses are independent, we can just calculate the probability of obtaining one head and repeating that 3 times. Obviously, the probability of getting a head for one toss is 1/2, our answer is 1/2⋅1/2⋅1/2=1/8
B. Suppose you have a fair coin: this means it has a 50% chance of landing heads up and a 50% chance of landing tails up. Suppose you flip it three times and these flips are independent. What is the probability that it lands heads up, then tails up, then heads up? So the answer is 1/8, or 12.5%.
~*"AUBA14"*~