Question 445640: 18. Suppose the code to a lock consists of there different numbers from the numbers 1 to 20, inclusive.
a. How many three-number codes are possible?
b. How many of the codes contain the numbers 6,13, and 17?
Answer by richard1234(7193)   (Show Source):
You can put this solution on YOUR website! a: Assuming order matters, the number of ways is 20P3 = 20*19*18.
b: There are 3! = 6 ways to arrange 6, 13, 17 to form different codes (e.g. 6-13-17 is different from 13-17-6, etc.)
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