Thursday, 10 January 2013

Math Page 2 Q6

No, we do not have to try each number up to 246. We just have to try the prime numbers: 2, 3, 5, 7, 11, 13. To find if 247 is a prime number, we must first square root it, then identify the prime numbers smaller or equal to its square root, after dividing every prime number, if it is divisible by one of the primes, then it is a composite number, otherwise, it is a prime number.

In this case,

Square root 247 = 15 (est. to whole number)
Primes under or equal to 15: 2, 3, 5, 7, 11, 13

Division (Use divisibility rules):
All are out. 

Conclusion: 247 is a prime number.

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