JEE Advanced2009MathematicsProbabilityActual
Paragraph: A fair die is tossed repeatedly until a six is obtained. Let X denotes the number of tosses required. Question: The conditional probability that X 6 given X>3 equals
Options
- A125 216
- B25 216
- C5 36
- D25 36
Correct answer
D. 25 36
Step-by-step solution
P((X 6) /(X>3)) aligned & = P((X>3) /(X 6)) P(X 6) P(X>3) & = 1 [ ( 5 6 )^5 1 6 + ( 5 6 )^6 1 6 + ] [ ( 5 6 )^3 1 6 + ( 5 6 )^4 1 6 + ] = 25 36 & aligned