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Math Help - counting problem

  1. #1
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    counting problem

    All possible two factor products formed from the numbers 1,2,3,4.... 200. The number of factors out of the total obtained which are multiples of 5 is?

    a. 5040
    b. 7180
    c. 8150
    d. none of these
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  2. #2
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    Re: counting problem

    Quote Originally Posted by swordfish774 View Post
    All possible two factor products formed from the numbers 1,2,3,4.... 200. The number of factors out of the total obtained which are multiples of 5 is?
    a. 5040
    b. 7180
    c. 8150
    d. none of these
    This is not a homework service. Please show what you have done.
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  3. #3
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    Re: counting problem

    hahaha!
    I didnt understand the question, what does number of factors mean
    non-multiples of 5 n 160 , multiples of 5 m 40 so, 160C1*40C1
    and multiples of 5 n * muliples of 5 so 40C2

    so 7180. but there is double counting, how do i remove that?

    why do you say 'this is not a homework service'? i use it to solve doubts and verify answers.
    Last edited by swordfish774; October 10th 2012 at 09:40 AM.
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  4. #4
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    Re: counting problem

    Quote Originally Posted by swordfish774 View Post
    why do you say 'this is not a homework service'? i use it to solve doubts and verify answers.
    When someone simply posts a list of problems with no comments, we assume that the person expects to get the answers just given to them.
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  5. #5
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    Re: counting problem

    okay, so can you please clarify the question? is the question about product of the factors? if yes then how do you go about it?
    because 25*8= 5*40
    this will lead to double counting..
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