a coin is tossed 3 times. If both heads and tails appear find the probability that exactly one tail appears.

i am using the conditional probability rule so p(probability of getting one tail | probability of getting one tail and one head )=

p(probability of getting one tail intersection probability of getting one tail and one head)/p(probability of getting one tail and one head)

i am having trouble finding the probability of getting one tail and one head as it could be in any order so i cant say (.5)^3