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Question: Answered & Verified by Expert
Three coins are tossed. If one of them shows tail, then the probability that all three coins show tail, is
MathematicsProbabilityJEE Main
Options:
  • A $\frac{1}{7}$
  • B $\frac{1}{8}$
  • C $\frac{2}{7}$
  • D $\frac{1}{6}$
Solution:
2201 Upvotes Verified Answer
The correct answer is: $\frac{1}{7}$
Let $E$ be the event in which all three coins shows tail and $F$ be the event in which a coin shows tail.
$\therefore F=\{H H T, H T H, T H H, H T T, T H T, T T H, T T T\}$
and $E=\{T T T\}$.
Required probability
$=P(E / F)=\frac{P(E \cap F)}{P(E)}=\frac{1}{7}$

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