Determine how many different computer passwords are possible if (a) the digits and letters can be repeated, and (b) if the digits and letters cannot be repeated.
i. 4 digits followed by 2 letters
ii. 5 digits followed by 1 letter.
iii. 3 digits followed by 3 letters
Answer)
1)
4 digits followed by 2 letters
When the digits and letters can be repeated
10*10*10*10*26*26
{As there are 10 digits (0-9) and 26 letters)
= 6760000
When the digits and letters cannot be repeated
10*9*8*7*26*25
= 3276000
2)
5 digits followed by one letter
When repeated
10*10*10*10*10*26 = 2600000
When not repeated
10*9*8*7*6*26 = 786240
3)
3 digits followed by 3 letters
When repeated
10*10*10*26*26*26 = 17576000
When not repeated
10*9*8*26*25*24
= 11232000
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