A coin is tossed twice, what is the probability that at least one tail occurs?

When a coin is tossed twice, the sample space is given by

S = {HH, HT, TH, TT}

Let A be the event of the occurrence of at least one tail.

Accordingly, A = {HT, TH, TT}

$\therefore \mathrm{P}(\mathrm{A})=\frac{\text { Number of outcomes favourable to } \mathrm{A}}{\text { Total number of possible outcomes }}$

$=\frac{n(\mathrm{~A})}{n(\mathrm{~S})}$

$=\frac{3}{4}$