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GATE 2017 ME (ME2) – Question 4

General Aptitude · Quantitative Aptitude: Arithmetic and Number Computation · 1 mark · Multiple choice

A couple has two children. If the older one is a boy, the probability that both are boys is ______.

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

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Show answer and explanation

Correct answer: (C) 1/2

Explanation

With independent equally likely sexes, conditioning on the older child being a boy leaves BB and BG as equally likely ordered outcomes. Only BB contains two boys, so probability is **1/2, C**. The1/3 result belongs to a different condition, at least one boy.