We know that,

Probability of occurrence of an event

Let T be tails and H be heads

Total possible outcomes = TTT, TTH, THT, HTT, THH, HTH, HHT, HHH

Desired outcomes are exactly one tail. So, desired outputs are THH, HTH, HHT

Total no.of outcomes are 8 and desired outcomes are 3

Therefore, the probability of getting exactly one tail

Conclusion: Probability of getting exactly one tail is