When a coin is tossed the possible outcomes are either a Head $\left( H \right)$ or Tail $\left( T \right)$.

Here, coin is tossed three times then the sample space contains,

$S{\text{ }} = {\text{ }}\left\{ {HHH,{\text{ }}HHT,{\text{ }}HTH,{\text{ }}THH,{\text{ }}TTH,{\text{ }}HTT,{\text{ }}TTT,{\text{ }}THT} \right\}$

And $n\left( S \right){\text{ }} = {\text{ }}8$.

(v) no head

Suppose $E$ be the event of getting no heads.

So, $n\left( E \right){\text{ }} = {\text{ }}1$

Then, the probability of the event is

$P(E) = \frac{{n(E)}}{{n(S)}}$

$P(E) = \frac{1}{8}$

(vi) $3$ tails

Suppose $F$ be the event of getting $3$ tails.

So, $n\left( F \right){\text{ }} = {\text{ }}1$

Then, the probability of the event is

$P(F) = \frac{{n(F)}}{{n(S)}}$

$P(F) = \frac{1}{8}$