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A little maths help?

  • 09-11-2010 11:06pm
    #1
    Hannahlu
    Closed Accounts Posts: 43 ✭


    Hi, can anyone help with this?
    How many numbers in the set {1, 2, . . . , 240} are divisible by (a) at least ONE of the
    numbers 6, 8, or 9? (b) precisely TWO of the numbers 6, 8, or 9?


Comments

  • #2
    Fremen
    Registered Users, Registered Users 2 Posts: 2,481 ✭✭✭Fremen


    What have you tried so far? Try focusing on one bit of part (a) first. How many of the numbers are divisible by 6? If you can't see it, try scaling down the problem to something you can write out in a sensible amount of time - maybe the numbers {1,...,30}


  • #3
    Fremen
    Registered Users, Registered Users 2 Posts: 2,481 ✭✭✭Fremen


    Sorry for backseat modding, but we'd rather you don't do that jaycee. I could have just given the answers, but that's not the point. I'm trying to teach rather than do someone's homework for them.


  • #4
    jaycee13
    Closed Accounts Posts: 3 ✭jaycee13


    Sorry Freman. Am only new was trying to help. Homework at this hour cant be good for someone. Sorry again


  • #5
    Hannahlu
    Closed Accounts Posts: 43 ✭Hannahlu


    thanks a million jaycee, i got that far but i just thought there was something more i had to do, its this whole area of maths that just confuses me, i never know when im finished, it always looks half done :confused: thank you, its such a relief, i can go to bed and sleep now :-)

    and sorry Fremen for not putting up my own attempts, its just so hard to put up on a forum let alone a piece of paper. But i'll try so in future, i don't just want my homework done, particularly when i have exams that i really want to do well in. its a great comfort to know theres people willling to help me understand here if i get stuck. :)


  • #6
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    jaycee13 wrote: »
    Sorry Freman. Am only new was trying to help. Homework at this hour cant be good for someone. Sorry again

    Please take the time to read the charter before you post again, thanks


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  • #7
    sponsoredwalk
    Registered Users, Registered Users 2 Posts: 3,038 ✭✭✭sponsoredwalk


    Hi, honestly this is not a new area of maths, this requires no more hard work
    than addition, subtraction, multiplication and division, don't be intimidated by
    it, assume you already know what to do and look at it again. Remember, it's
    an extremely simple idea, but I understand your mind can get carried away
    thinking it's some weird idea, happens to me all the time :o


  • #8
    Fremen
    Registered Users, Registered Users 2 Posts: 2,481 ✭✭✭Fremen


    For part b, what property does a number need to have to be divisible by 6 and 9 but not by 8? Hint: think of prime factors.


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