This "Probability" problem has stumped me for several weeks:

If I randomly select a 20 character password from a set of 256 characters composed of:

4 sets of lower case letters (104),

3 sets of Upper case letters (78),

7 of each number in 0..5 (42) and

8 of each number in 6..9 (32)

total (256)

What are the chances a second random 20 character selection will match the first?

Notes:

P(M,N) means the probability of M items taken N at a time, order counts.

C(M,N) means the # of combinations of M items taken N at a time (order is n/a)

Many thanks . . .

- Ed

My first estimate is odds of 1 in

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