Question

Which of these numbers is prime? Explain why or why not.

407
409
411
413

Answer 1

http://en.wikipedia.org/wiki/Prime_number

So ... which of these can be <b>divided <u>evenly</i> only by itself and 1</b>?

??</u>

Answer 2

Which one(s) are evenly divisible by prime numbers less than the sqrt of the number. The square root of the largest is 20.32. Since they are all odd, 2 is not a divisor, Therefore, division by 3, 7, 11, 13, and 19 are the only tests.