jmc

The probability of getting two tails followed by one head is ${\left(\frac{1}{2}\right)}^3=\frac{1}{8}$. The probability of getting a tail followed by a head followed by a tail is also ${\left(\frac{1}{2}\right)}^3=\frac{1}{8}$. Finally, the probability of getting a head followed by two tails is ${\left(\frac{1}{2}\right)}^3=\frac{1}{8}$ as well. In total, the probability of getting two tails and one head is $\frac{1}{8}+\frac{1}{8}+\frac{1}{8}=\boxed{\frac{3}{8}}$.