GATE 2012 CS (CS1) – Question 43

Engineering Mathematics · Probability and Statistics · 2 marks · Multiple choice

Roll a fair six-sided die once. If the first value is 1,2 or 3, roll again. What is the probability the total rolled value is at least six?

$10/21$
$5/12$
$2/3$
$1/6$

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Show answer and explanation

Correct answer: (B) $5/12$

Explanation

A first roll of six succeeds immediately, probability 1/6. For first rolls 1,2,3, the second must be at least 5,4,3 respectively, giving 2+3+4=9 successful ordered two-roll outcomes, each probability 1/36. Total is 1/6+9/36=5/12, B.

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