A briefcase has a three-digit lock code that does not include zero as a digit.What is the probability that the lock code consists of all even digits if the same digit is not used more than once in the lock code?

Since zero is not allowed, the code’s digits come from 1 through 9. There are 9 × 8 × 7 = 504 possible codes when no digit is repeated. The available even digits are 2, 4, 6, and 8, so the number of three-digit codes using distinct even digits is 4 × 3 × 2 = 24. Thus the probability is 24 out of 504, choice A.

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