



 
Hi Edward, There are 8 possible 1 digit numbers you can make. Each one of them you can extend to a 2 digit number in 7 ways since you have 7 digits left to choose from. Thus there are 8 × 7 possible 2 digit numbers. In the same way, each of the 2 digit numbers can be extended to a 3 digit number in 6 ways since there are 6 digits to choose from. Thus there are 8 × 7 × 6 possible 3 digit numbers. Continue in the same way,  


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