SOLUTION: 1) A telephone number consists of seven digits. How many different telephone numbers exist if each digit appears only one time in the number? How would I solve this type of problem

Question 484339: 1) A telephone number consists of seven digits. How many different telephone numbers exist if each digit appears only one time in the number? How would I solve this type of problem?

Answer by sudhanshu_kmr(1152) (Show Source): You can put this solution on YOUR website!

For first digit, we can use any one of 9 digits, except 0 i.e (1,2,3,...9)
for second digit, we can use any one of : 9 (except which is on first position)
similarly, for third digit, we can use any one of : 8 (except first and second)
and so on......
number of possible numbers = 9*9*8*7*6*5*4 = 544320

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