Question:
Total number of 6-digit numbers in which only and all the five digits $1,3,5,7$ and 9 appear, is:
Correct Option: , 4
Solution:
Five digits numbers de $1,3,5,7,9$
For selection of one digit, we have ${ }^{5} C_{1}$ choice.
And six digits can be arrange in $\frac{6 !}{2 !}$ ways.
Hence, total such numbers $=\frac{5.6 !}{2 !}=\frac{5}{2} \cdot 6 !$
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