Using the Fundamental Counting Theorem, it is found that:
a) 256 codes are possible.
b) The probability is [tex]\frac{1}{256}[/tex].
It is a theorem that states that if there are n things, each with [tex]n_1, n_2, \cdots, n_n[/tex] ways to be done, each thing independent of the other, the number of ways they can be done is:
[tex]N = n_1 \times n_2 \times \cdots \times n_n[/tex]
There are 4 keys, each with 4 options, hence the parameters are:
[tex]n_1 = n_2 = n_3 = n_4 = 4[/tex].
Then the number of codes is:
[tex]N = 4^4 = 256[/tex]
And the probability is:
[tex]p = \frac{1}{256}[/tex].
More can be learned about the Fundamental Counting Theorem at https://brainly.com/question/24314866
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