A computer password can be 5 - 6 characters. The password must contain at least 1 digit. All other characters must either be digits or lower case letters. How many unique passwords exists?
For making a five characters password we have:
Fix the ist place in the five string password with a digit then it has 10 (0 to 9) choices.
Now for the remaining four places we have to choose out of 26 (lower case letters) and 9 remaining choices.That is we have (26+10=36) coices for 4 places i.e we have combinations.
Hence we have all five cheracter password.
For making 6 cherecter passwors we have the combinations passwords.
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