JEE Main202126 Aug 2021Evening ShiftMathematicsProbabilityActual
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 :
Options
- A25 36
- B5 6
- C11 36
- D125 216
Correct answer
A. 25 36
Step-by-step solution
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