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Thread: Very basic question (I've only recently started learning Mathematics beyond multiplication!)

  1. #1 Very basic question (I've only recently started learning Mathematics beyond multiplication!) 
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    Hey all, I'm a little confused on this. I am following a book called 'Foundation Mathematics' and using it in conjunction with Khan Academy.

    When you try to find the greatest common factor for 2 (hypothetical) numbers, if for example they have the following prime numbers as factors:

    hypothetical number one: 3, 3, 5, 7
    hypothetical number two : 3, 5, 11

    There are then two primes in common (3 and 5). In the book I am following, it suggests that each of the matching primes are multiplied, and in this case the primes in common are 3 and 5, and to find the GCF you do 3x5= 15 so 15 = HCF, whereas on Khan Academy it suggests the HCF is simply five...

    What am I missing??

    Thanks!


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    Administrator KALSTER's Avatar
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    Typo? As far as I know, 15 is the correct answer.


    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    Quote Originally Posted by KALSTER View Post
    Typo? As far as I know, 15 is the correct answer.
    Thanks Kalster, and, should there be three common primes (3,5,11) would the answer then be 165? It just grows as more common primes appear? Sorry for such a simple question but I can't stand not getting the basics down, and I am a new learner.
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    Administrator KALSTER's Avatar
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    No problem. Your questions are welcome.

    Yes, 165 would be the answer. Similarly to find the common factor of three numbers, then it works the same: If 2, 3 and 4 are common between the factors of three numbers, then the answer is 24. If the 2, 3 and 3 are common factors, then the answer is 18.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  6. #5  
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    Much appreciated, that has completely cleared things up for me Thank you!
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    Pleasure.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

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