A store manager would like to set the three-digit code of the store’s new safety vault. How many possible 3-digit code choices does he have if he can pick digits from 0 to 9 with repetition allowed?

(D) 1,000


This is the easiest type of question when it comes to permutation and combination problems.
While we’d be quick to call this a combination question (because we’re familiar with “combination” locks), this is actually a permutation type of question.
Combination refers to problems where the order of things (or digits in this case) is not important.
Permutation refers to problems where the order or position of things is important.
Simply use the formula for permutations when repetition is allowed:
P is the number of permutations possible, n is the number of things to choose from and r is the number of things we choose.

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