The correct option is A 67
The sample space of the given experiment will be:
S={HHH,HHT,HTH,THH,HTT,THT,TTH,TTT}
Here, E: atmost two tails
And F: atleast one tail
E={HHH,HHT,HTH,THH,HTT,THT,TTH} and F={HHT,HTH,THH,HTT,THT,TTH,TTT}
So, P(E)=78,P(F)=78,P(E∩F)=68=34
Now we know that
By definition of conditional probability
P(E/F)=P(E∩F)P(F)
⇒P(E/F)=3/47/8=67