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

(ix) at most two tails

Suppose $I$ be the event of getting at most $2$ tails.

So, $n\left( I \right){\text{ }} = {\text{ }}7$

Then, the probability of the event is

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

$P(I) = \frac{7}{8}$