//------------------------------//
// The Answer 28 
// Story: Life is a Test: A Series of Pony Logic Puzzles 
// by Brony_of_Brody 
//------------------------------//

You'll need at least thirteen attempts to assuredly open the safe.

We have three keys and three locks, and so we have six different ways we can arrange the keys to assigned locks. Depending on how they're arranged, one of five things can happen:




Nothing happens.

 The first lock changes state.

The second lock changes state.

The third lock changes state.

They all change state.



We also have three locks in two possible states: locked or unlocked. We therefore have eight different possibilities when it comes to how the locks could start off as. And because we don't know how each lock was at the start, we have to go through ALL possible combinations to guarantee the safe opens. So we can't do any better than eight tries, but we can make sure we don't do worse than thirteen. Try opening it by inserting each of these keys in the locks ordered 1-3 in this order:

ABC, ABC, BCA, CAB, ABC, BCA, ABC, ACB, BAC, ACB, CBA, BAC, ACB.