Question

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

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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How many 3-letter passwords can be formed from the letters A
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