Answer:
X = {0, 1, 2, 3, 4}
Step-by-step explanation:
If X is the number of nonzero digits in a 4-digit PIN with no restriction on the digits, the pin can have up to 4 nonzero digits.
Let's see some examples:
If the PIN is 0000 then X = 4
If the PIN is 2045 then X = 3
If the PIN is 7546 then X = 0
From the previous examples, we can see that the possible values for X are 0, 1, 2, 3, 4.
Thus X = {0, 1, 2, 3, 4}
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