# Prime numbers: How would you do this efficiently?

Which of the following integers is prime: 187, 287, 387, 487, or 587? I can calculate it by hand, but that would take a long time. Is there an easier way? I noticed the numbers only differ 100 from each other, but can I use that fact? Exactly one of these must be prime.

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Is it given that exactly one of these numbers must be prime? –  Myself Jan 31 '12 at 11:32
Sorry, forgot that fact, that's true. –  Kevin Jan 31 '12 at 11:44
The Divisibility rules will be helpful in this case. –  userxxxxx Jan 31 '12 at 12:56
Also, the question is not correct, since two of these numbers are prime (factmonster.com/math/numbers/prime.html). –  userxxxxx Jan 31 '12 at 13:05
–  Frank Science Jan 31 '12 at 14:27