Question

(PLS HELP!!!) Fundamental Principles of Counting:

Lindsey has to set up a four-digit password on her phone. The password could use any of the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9. She cannot repeat the same digit. How many different passwords are possible?

Answer 1

Answer: 3024

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Work Shown:

9*8*7*6 = 3024

The first slot has 9 choices. The next slot has 8 choices since we cannot reuse whatever we picked for the first slot. We keep counting down until we fill up the four slots. So we'll be multiplying out four values as shown above.

As an alternative, you can use the nPr permutation formula with n = 9 and r = 4 to get the same answer.