A die is thrown twice and the sum of the numbers appearing is observed to be 6. What is the conditional probability that the number 4 has appeared at least once?

Explanation

Let A= sum of the numbers appearing on two dice is 6
=(1,5),(5,1),(2,4),(4,2),(3,3)

So,
n(A)=5



B= number 4 has appeared at least once

=(1,4),(4,1),(2,4),(4,2),(3,4),(4,3),(4,4),(4,5),(5,4),(4,6),(6,4)

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