# find the prime factor of two numbers

• Mar 4th 2010, 06:18 PM
pandakrap
find the prime factor of two numbers
Q: find the sum of all common prime factors of 51 and 204

so I found 1, 3, 17 for the common prime factors of those two numbers. but does "1" count and a common prime factor?

thanks you
• Mar 4th 2010, 06:27 PM
tonio
Quote:

Originally Posted by pandakrap
Q: find the sum of all common prime factors of 51 and 204

so I found 1, 3, 17 for the common prime factors of those two numbers. but does "1" count and a common prime factor?

thanks you

1 is not considered a prime number...and how come 20 or 21??? It is straightforward that neither divides 51...(Itwasntme)

We have $\displaystyle 51=3\cdot 17\,,\,\,204=2^2\cdot 3\cdot 17$ ....look carefully at these two prime factorings and now: what's the greatest common divisor of 51 and 204?

Tonio
• Mar 5th 2010, 02:52 AM
HallsofIvy
I think you misread the post, Tonio. The question was NOT "what is the greatest common factor". The question was "what is the sum of the common prime factors. If the only common prime factors are 3 and 17 then the sum is 20.
• Mar 5th 2010, 05:04 AM
tonio
Quote:

Originally Posted by HallsofIvy
I think you misread the post, Tonio. The question was NOT "what is the greatest common factor". The question was "what is the sum of the common prime factors. If the only common prime factors are 3 and 17 then the sum is 20.

That "I misread the post" is an understatement: I must have been high, drunk or both when I dealt (?) with it. This is funny since I do no drugs at all and only drink alcoholic beverages once in a while, and also that in very minimal quantities.

I hope the OP didn't get too confused with my nonsense.

Tonio