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Math Help - factors

  1. #1
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    Question factors

    how do you find out all the factors of a number in 10 seconds?? i take ages to find out all of the factors - there has to be an easier way!! please help me
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  2. #2
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    Hi Kate

    Quote Originally Posted by kate
    how do you find out all the factors of a number in 10 seconds?? i take ages to find out all of the factors - there has to be an easier way!! please help me
    Hi

    I don't understand the question. Can you explain what you have so far?

    Thanks
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  3. #3
    Member
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    Nov 2005
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    Wethersfield, CT
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    92
    Hi:
    Ex 1: List all factors of 1248.

    Solution:
    Check 1 (trivial): Trivial factors are 1 and 1248.
    Check 2: 1248/2=624. Thus two factors are 2 and 624.
    Check 3: 1248/3=416 " " " " 3 and 416
    Check 4: 1248/4=312 " " " " 4 and 312
    Check 5: no
    Check 6: 1248/6=208 " " " " 6 and 208
    Check 7: no
    Check 8: 1248/8=156 " " " " 8 and 156
    Check 9: no
    Check 11: no
    Check 12: 1248/12=104 " " " " 12 and 104
    etc.

    Factors of 1248:{1, 1248, 2, 624, 3, 416, 4,3 12, 6,
    208, 8, 156, 12, 104, 13, 96, 16, 78, 24, 52, 26, 48, 32, 39}.

    Hint: You can stop your search at sqrt(n). In the present case, sqrt(1248)=35.327... Therefore check natural numbers to 35.

    Method2 (easy):


    Use mod key on calculator.


    Ex 2: List factors of 330.


    Solution:

    Enter 330 into memory (330 STO).


    Sqrt(330) = 18.17... Therefore check up to 18.


    On calculator, systematically enter (MR)mod(k) for all k in {1, 2, 3, ..., 18} (MR <=> MEM-RECALL). You can isolate factors by utilizing the fact that k is a factor of n iff n_mod(k)=0. For example, 330mod(8) = 2. Thus 8 is not a factor of 330. 330mod(15)=0. Thus 15 is a factor, as is 22 (330/15=22).


    Regards,


    Rich B.
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