The sample space is
{HHH,HHT,HTH,HTT,THH,THT,TTH,TTT}
The outcomes with 1 tail and 2 heads are in red.
That's 3 ways out of 8, which means on the average it will
occur about 3/8ths of the time, and therefore the probability
of 1 tail and 2 heads is 3/8.
Edwin