1
DSCI
2710
Permutation and
Combination
How Many 4-digit PIN Numbers
are Possible?
We need to know what are the possible
values for each digit.
We need to know if a number can be
repeated.

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Assume Repetition Is Allowed
Assume that each PIN digit can be
chosen from 0 to 9.
If repetition is allowed , then the
number of codes is
10 * 10 * 10 * 10 = 10
4
= 10,000
Assume No Repetition Is
Allowed
Si
di it
t b
Since a digit cannot be
repeated, the number of
choices decreases each time.
The number of possible codes
is
10 * 9 * 8 * 7 = 5040.