A fair die is tossed until six is obtained on it. Let X be the number of required tosses, then the conditional probability P ( X ⩾ 5 ∣ X 2 ) is :

Question

A fair die is tossed until six is obtained on it. Let X be the number of required tosses, then the conditional probability P ( X ⩾ 5 ∣ X > 2 ) is :, 25 36, 5 6, 11 36, 125 216

MARKS App · Accepted Answer

P x ≥ 5 x > 2 = P ( x ≥ 5 ∩ x > 2 ) P ( x > 2 ) = 5 6 4 1 6 + 5 6 5 1 6 + . . . . . . . ∞ 5 6 2 · 1 6 + 5 6 3 1 6 + … … … . ∞ = 5 6 4 · 1 6 1 - 5 6 5 6 2 1 6 1 - 5 6 = 5 6 2 = 25 36

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