JEE Main 2019 (Online) 12th January Morning ShiftQuestion 1
In a random experiment, a fair die is rolled until two fours are obtained in succession. The probability that the experiment will end in the fifth throw of the die is equal to :
Probability
Solution
Throws $4,5$ are fours, throw $3$ is not a four ($5$ ways), throws $1,2$ are not both fours ($35$ ways). Count $=175$, probability $\frac{175}{6^5}$.