There are 720 ways of codes are possible.
Explanation:
Given that the code consists of 3 digits, none of which is repeated.
We need to determine the codes that are possible.
The possible ways of codes can be determined using the permutation formula,

where n is the number of choices and r is the number chosen.
Hence, substituting
and
, we have,

Simplifying, we get,


Cancelling the common terms, we get,

Multiplying, we get,

Thus, there are 720 ways of codes are possible.