Lets denote HH after getting heads and TT after getting tails as toss a result. Then after tossing 33 coins we will get following probable cases,

S={HHH,HHT,HTH,THH,HTT,THT,TTH,TTT}

and chances of getting at least one tail if one of following case occurs

ST={HHT,HTH,THH,HTT,THT,TTH,TTT}.

Therefore, probability of getting at least one tail after tossing 3 coins is \(\displaystyle{\left(\frac{{\left|{S}\right|}}{{\left|{S}{t}\right|}}\right)}=\frac{{7}}{{8}}.\)

S={HHH,HHT,HTH,THH,HTT,THT,TTH,TTT}

and chances of getting at least one tail if one of following case occurs

ST={HHT,HTH,THH,HTT,THT,TTH,TTT}.

Therefore, probability of getting at least one tail after tossing 3 coins is \(\displaystyle{\left(\frac{{\left|{S}\right|}}{{\left|{S}{t}\right|}}\right)}=\frac{{7}}{{8}}.\)