Question 160991
a.)At most one head means one head or no head.
4 outcomes:HTT THT TTH TTT
P(at most 1 H)=4/8=1/2
 
b.)At most two tails means two tails, one tail or no tail. Or simpler, not three tails. 
Since only TTT has 3 tails, then all the rest have at most 2 tails.
P(at most 2 T)=7/8