Video: Finding the Greatest Prime Number between Two Given Numbers

What is the greatest prime number between 15 and 24?

01:44

Video Transcript

What is the greatest prime number between 15 and 24?

Let’s start by identifying which numbers are prime between 15 and 24. Or better yet, let’s start by eliminating numbers we know are not prime. Any number on this number line that’s even is not a prime number because it’s divisible by two. So we can eliminate 16, 18, 20, 22, and 24.

I also know that 15 is divisible by three, which means 15 can’t be a prime number. 21 is divisible by three. 17 has no other factors; it’s only divisible by one and itself. It’s a prime number. 19 has no other factors; it’s only divisible by one and itself. It is a prime number. The same thing is true for 23. 23 is not divisible by anything except for one and itself.

On our number line, we’ve identified three prime numbers: 17, 19, and 23. Our question is asking what is the greatest prime number between 15 and 24.

The greatest prime number between 15 and 34 [24] is 23.

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