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GATE 2014 EC (EC1) – Question 10

General Aptitude · Analytical Aptitude: Logical Reasoning and Deduction · 2 marks · Multiple choice

Three coins have faces HH, TT and HT. Choose one at random and toss it; the result is a head. Find the probability that its other face is a tail.

  1. 1/4
  2. 1/3
  3. 1/2
  4. 2/3

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Show answer and explanation

Correct answer: (B) 1/3

Explanation

The three equally likely coins are HH,TT and HT. After observing a head, the equally likely compatible face outcomes are the two head faces of HH and the single head face of HT. Only the HT outcome has a tail on the other side. Hence the conditional probability is **1/3,B**, not1/2.