Step by step
The question
Question: is 17 a prime number?
Is 17 prime?
A prime number has exactly two factors: 1 and itself.
So we look for any other number that goes into 17.
prime: only 1 and itself go in
1 Try dividing
Does 2 go in?
17 divided by 2 is 8, with 1 left over.
So 2 is not a factor.
= 17 ÷ 2 = 8 r 1 ✗
r 1 = 1 left over
Does 3 go in?
17 divided by 3 is 5, with 2 left over.
So 3 is not a factor.
= 17 ÷ 3 = 5 r 2 ✗
Does 4 go in?
17 divided by 4 is 4, with 1 left over.
So 4 is not a factor.
= 17 ÷ 4 = 4 r 1 ✗
Next is 5.
But 5 times 5 is 25, more than 17.
So nothing bigger can go in.
We stop.
5 × 5 = 25 > 17 → stop
2 Decide
Nothing goes in, only 1 and 17.
So 17 is prime.
= 17 is prime
Let's look back.
First: try dividing.
Last: decide.
Answer
= 17 is prime