You have 10 numbers to choose from, and you're choosing 4 from that pool. Order of the numbers matters, because having 1234 as a PIN is not the same having it be 1324, so we're counting the number of permutations of 10 digits taken 4 at a time. So there are

possible PINs that can be made.
0. 24's opposite is -24. 24 more than -24 is 0.
Answer:
It is 725/1000.
Step-by-step explanation:
The fraction can be simplified but that will result in a loss of information about its accuracy.
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