Prime Factor PuzzleDate: 10/24/2003 at 10:43:56 From: Stephen Subject: prime factors The two prime factors of a number are greater than 12 but less than 25. The number is greater than 300 but less than 400. What is the number? What are the factors? Date: 10/25/2003 at 19:49:33 From: Doctor Ian Subject: Re: prime factors Hi Stephen, Let's look at a smaller version of the problem. The two prime factors of a number are greater than 3 but less than 10. The number is greater than 30, but less than 40. What are the factors? First, we have to find all the prime numbers between 3 and 10. The first several prime numbers are 2, 3, 5, 7, 11, 13, ... so the ones we're interested in are 5 and 7. Now, how many numbers c can be make with those prime factors? x 5 7 -------- | 5 | 25 35 | 7 | - 49 ^ |_________________ 7x5 is the same as 5x7 Of all these, the only product between 30 and 40 is 35, so the prime factors we must be looking for are 5 and 7, and the number is 35. Does this make sense? Your problem is like this, but with different numbers. Can you use the solution above as a model for solving your problem? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/