1. One of the following numbers is prime. Which is it?
A $2017-2$
B $2017-1$
C 2017
D $2017+1$
E $2017+2$
SolUtion
C
We see that:
$2017-2=2015$ and 2015 is a multiple of 5. So $2017-2$ is not prime.
$2017-1=2016$ and 2016 is a multiple of 2. So $2017-1$ is not prime.
$2017+1=2018$ and 2018 is a multiple of 2. So $2017+1$ is not prime.
$2017+2=2019$ and 2019 is a multiple of 3. So $2017+2$ is not prime.

We are told that one of the given options is prime. We may therefore deduce that the remaining option, 2017 , is prime.