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Joint Entrance Examination
Mathematics
Probability
Question 339
Question 339 of 417
Medium
MCQ
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 :
A
\[{{200} \over {{6^5}}}\]
B
\[{{225} \over {{6^5}}}\]
C
\[{{150} \over {{6^5}}}\]
D
\[{{175} \over {{6^5}}}\]
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Official solution
\[\underline {} \,\,\,\underline {} \,\,\,\underline {} \,\,\underline 4 \,\,\underline 4 \] \[{1 \over {{6^2}}}\left( {{{{5^3}} \over {{6^3}}} + {{2{C_1}{{.5}^2}} \over {{6^3}}}} \right) = {{175} \over {{6^5}}}\]
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