Question

Three coins are tossed. If one of them shows tail, then the probability that all three coins show tail, is

• A. $\frac { 1 } { 7 }$
• B. $\frac { 1 } { 8 }$
• C. $\frac { 2 } { 7 }$
• D. $\frac { 1 } { 6 }$

Answer 1

Answer: (A)

$\frac { 1 } { 7 }$

Answer 2

Let $E$ be the event in which all three coins shows tail and $F$ be the event in which a coin shows tail.

∴ $F = \{ H H T , H T H , T H H , H T T , T H T , T T H , T T T \}$

and $E = \{ T T T \}$.

Required probability $= P ( E / F ) = \frac { P ( E \cap F ) } { P ( E ) } = \frac { 1 } { 7 }$