Circle the prime numbers in the following set of numbers. Show your work.

953, 1,427, 2,971

I can tell whether each number is prime but I am having a hard time with individual numbers

1 answer

Just start trying factors, up to the square root of the number.

3|953? no
clearly 5 is not a divisor
7|953? no
trying all the primes up to 30, we see that there are no factors of 953. It is prime.

We stop at the square root, because if there is a factor greater than √n, then there is another factor less than √n, since

√n * √n = n