Question 1050011
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Using the digits 0-9, how many six digit numbers can be formed if no digits can be repeated?
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1.  Any of the digits from 1 to 9 in the leftmost position.         9 options.

2.  Any of remaining 9 digits in the next to the right position.    9 options.

3.  Any of remaining 8 digits in the next to the right position.    8 options.

4.  Any of remaining 7 digits . . .                                 7 options.

. . . . And so on . . . 

6.  Any of remaining 5 digits in the rightmost, 6-th position.      5 options.


In all, there are 9*(9*8*7*6*5) = 136080 such numbers.
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