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6.Permutation and Combination
medium
$0,1,3,5,7$ तथा $9$ अंकों से, $10$ से विभाजित होने वाली और बिना पुनरावृत्ति किए कितनी $6$ अंकीय संख्याएँ बनाई जा सकती हैं ?
A
$120$
B
$120$
C
$120$
D
$120$
Solution
A number is divisible by $10$ if its units digits is $0 .$
Therefore, $0$ is fixed at the units place.
Therefore, there will be as many ways as there are ways of filling $5$ vacant places $\boxed{}\,\boxed{}\,\boxed{}\,\boxed{}\,\boxed{}\,\boxed0\,$ in succession by the remaining $5$ digits (i.e., $1,3,5,7$ and $9$ ).
The $ 5$ vacant places can be filled in $5 !$ Ways.
Hence, required number of $6 -$ digit numbers $=5 !=120$
Standard 11
Mathematics