Prime Problem Solving

[Stephanie6564]

HELP! :? It has been over 25 years since I did any math problems and my 9yr old needs help! Here is the problem:

"Jeff is thinking of a number between 30 and 40 that is prime. If the digits of this prime number are added together, the sum is 10. What number is Jeff thinking of?"

I am drawing a major blank here1 ANY help?

 

[TchrWill]

It has been over 25 years since I did any math problems and my 9yr old needs help! Here is the problem:

"Jeff is thinking of a number between 30 and 40 that is prime. If the digits of this prime number are added together, the sum is 10. What number is Jeff thinking of?"

I am drawing a major blank here1 ANY help?

How many prime numbers are there between 30 and 40?

What are they?

Which one has digits that add up to 10?

 

[DrSteve]

A prime number is a positive integer with exactly 2 factors.

A "quick" way to determine if a positive integer is prime is to take the square root of the number, and check if the number is divisible by all primes up to that square root. for example, let's check if 41 is prime. The \(\displaystyle \sqrt{41}\) is approximately 6.4. So we only need to check if 41 is divisible by 2, 3 and 5 which it is not. So 41 is prime. But 4+1 is not 10. So 41 is not the number you're looking for.

 

[Deleted member 4993]

Or look at it from the other side:

How many number between 30-40 have digits that add upto 10? - only one

Is that number a prime?

 

[Denis]

Or look at it from the other side:

How many number between 30-40 have digits that add upto 10? - only one

Is that number a prime?

NO! That's too easy :shock:

 

[Alurkz]

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