Question

You are asked to create a new computer password made up of 4 digits followed

by 3 letters.
Determine how many different computer passwords are possible if digits and
letters cannot be repeated.

Answer 1

Answer:if we start with 26 letters in the English/Latin alphabet: 26*25*24*23*

and modern Arabic numerals 0–9,

10*9 do the math by multiplying all

Number of dispositions of 4 letters without repetitions of the alphabet (26 letters): 26*25*24*23=358800. 2-digit numbers without repetitions:10*9=90. Number of passwords with 4 letters and 2-digit number without repetitions:

a) if the 2-digit numbers must be in one single position (examples:….XB73DY……..GZ57FE): 358800*90 = 32,292,000.

b) if the 2-digit numbers can be in each of the 5 possible positions (ex.:…73XBDY…X73BDY..XB73DY..XBD73Y..XBDY73…) 5*358800*90=161,460,000.

c) if both digits can be in (C6;2) = 6*5/2= 15 positions (ex.: 7XB3DY…X73BDY…..) 15*358800*90=484,380,000.26*25*24*23*10*9 = 32,292,000

Explanation: