A password is 4 characters long and must consist of 3 letters and one number. If letters cannot be repeated and the password must end with a number, how many possibilities are there?

Because the password must end with a number, the final position has 10 choices. The first three positions must be distinct letters, giving 26 × 25 × 24 choices. Thus there are 26 × 25 × 24 × 10 = 156,000 passwords, which is choice C, “156,000.”

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