SOLUTION: Suppose any 7-digit number whose first digit is neither 0 nor 1 can be used as a telephone number. a. How many telephone numbers are possible if repetition of digits is allo

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Question 1065677: Suppose any 7-digit number whose first digit is neither 0 nor 1 can be used as a telephone number.
a. How many telephone numbers are possible if repetition of digits is allowed? b. How many are possible if repetition of digits is not allowed?
c. A number such as 911-_ _ _ _ “WASTES” a lot of phone numbers. How many phone total numbers are wasted due to 911, 411 & 555?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a) N=8%2A9%2A8%2A7%2A6%2A5%2A4=483840
b) N=8%2A10%5E6=8000000
c) Well wasted is kind of subjective, you lose 10000 numbers for each 3 digit special prefix (assuming repetition, N=10%2A10%2A10%2A10
or 50400 without repetition). So 30000 lines wasted just to have potentially lifesaving response.