Question
A password consists of 2 letters and 2 digits (0-9). The letters and digits cannot be repeated. How many passwords are possible?
Answers
bobpursley
C=27!/25! * 10!/8! * 4!/2!2!
The last term represents the number of permuations of two letters, two numbers can be done (six ways).
The last term represents the number of permuations of two letters, two numbers can be done (six ways).
Reiny
my approach:
first lets choose 2 letters and 2 numbers,
that is C(26,2)*C(10,2)
= 325*45
= 14625
let's consider one of these, say, DK45
now that could be arranged in 4! ways
so the total number of passwords is
14625*4! = 351000
bobpursley, when did they introduce that 27th letter?
first lets choose 2 letters and 2 numbers,
that is C(26,2)*C(10,2)
= 325*45
= 14625
let's consider one of these, say, DK45
now that could be arranged in 4! ways
so the total number of passwords is
14625*4! = 351000
bobpursley, when did they introduce that 27th letter?
zara
A student can create a 3 digit computer password from the numbers 0 to 9. If the digits cannot be repeated, what is the probability of someone guessing the correct password?