Question

9. Determine whether or not the number 257 is prime.

Answer 1

Answer:

257 is prime.

Step-by-step explanation:

To evaluate if a number is prime, we just need to evaluate it for the prime numbers that are equal or lesser than the said number's square root.

In this case, √257 = 16.03 so we just need to see if 257 is divisible by 2, 3, 5, 7, 11 and 13 (the prime numbers that come before 16)

• 257 is odd, so it is not divisible by 2.

• The sum of its digits is 14, therefore, it is not divisible by 3.

• 257 ends in 7, therefore it's not divisible by 5.

• 257/ 7 = 36.71 so it's not divisible by 7.

• 257/ 11 = 23.36 so it's not divisible by 11

• Finally 257 / 13= 19.76 so it's not divisible by 13.

Therefore, 257 is prime.