How can you tell if a number is prime?

A prime number has only two factors.

1. Which of the following numbers is divisible by 2 (and definitely not prime)?

17, 26, 101, 924, 1000000, 39

2. Which of the following numbers is divisible by 3 (and definitely not prime)?

16, 51, 39, 243, 117, 2014, 2016

3. Which of the following numbers is divisible by 9 (and definitely not prime)?

16, 51, 39, 72, 243, 117, 2010, 2014, 2016

4. Which of the following numbers is divisible by 7?

18, 28, 43, 45, 49, 52, 63, 72, 87, 91, 98

5. Which of the following numbers is divisible by 15?

16, 51, 39, 72, 243, 117, 2010, 2014, 2016

Answers