Sample space =
⎡⎢
⎢
⎢
⎢
⎢
⎢⎣TTHT,TTTH,TTTT,TTHHTHHT,THTH,THTT,THHHHTHT,HTTH,HTTT,HTHHHHHT,HHTH,HHTT,HHHH⎤⎥
⎥
⎥
⎥
⎥
⎥⎦
Total number of outcomes =16
Favourable outcome for getting all heads ={HHHH}
Number of favourable outcomes =1
Probability of getting all heads =Number of favourable outcomesTotal number of outcomes=116
P(atleast one tail) = 1 - P (heads only)
⇒ P(Atleast one tail) =1−116
=1516
Favourable outcomes for 2 heads and 2 tails ={HHTT,TTHH,THHT,HTTH,THTH,HTHT}=6
P(2 heads and 2 tails) =616
=38