SOLUTION: every telephone number consists of 7 digits .how many telephone numbers are there which do not include any other digits but 2,3,5,7

Question 777926: every telephone number consists of 7 digits .how many telephone numbers are there which do not include any other digits but 2,3,5,7
Answer by ramkikk66(644) (Show Source): You can put this solution on YOUR website!
First digit can be any of the 4 digits and hence be chosen in 4 ways.
Second digit also can be any of the 4 (since repeated digits are allowed).
Similarly, each of the 7 digits can be chosen in 4 ways.
Hence the total number of possible numbers = 4*4*4*4*4*4*4 = 4^7 = 16384.
Hope you got it :)

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