Question

A coin is tossed three times, if head occurs on first two tosses, find the probability of getting head on third toss.

Answer 1

Consider the given events.
A = Getting head on third toss
B = Getting head on first two tosses

Clearly,
A = {(H, H, H), (H, T, H), (T, H, H), (T, T, H)}
B = {(H, H, H), (H, H, T)}

\[\text{ Now } , \]
\[A \cap B = \left\{ H, H, H \right\}\]
\[ \therefore \text{ Required probability }  = P\left( A/B \right) = \frac{n\left( A \cap B \right)}{n\left( B \right)} = \frac{1}{2}\]