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Problems on integers

  1. Oct 6, 2011 #1
    Q 1:-
    Given a sequence kn=[(1+(-1)^n)+1]/5n+6..
    find the no of terms of the sequence kn which will satisfy the condition kn lies between 1/100 and 39/100.

    Q 2:-
    Find the sum of all the irreducable fractions between 10 and 20 with a denominator of 3

    Q 3:-
    Find all pairs of natural no s whose greatest common divisor is 5 and L.C.M is 105

    i could really not do much about these so please help! Any assistance appreciated ..
     
  2. jcsd
  3. Oct 6, 2011 #2

    HallsofIvy

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    Well, what did you do? And why was this not posted under "homework help"?
     
  4. Oct 6, 2011 #3
    See i don't know anything about forums..like where do we even get the section "homework help"..! anyways that's not the issue here.
    For the first question i tried to make the denominator 100 for which i got n in fraction now that if i put in numerator then in all probability it becomes a question of complex numbers which i don't know.For the second i am getting the answer uncountable or infinity and i don't know third
     
  5. Oct 6, 2011 #4

    uart

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    There are none, as all the terms in the sequence are greater than 6.
     
  6. Oct 6, 2011 #5

    SammyS

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    I suppose you mean kn=[(1+(-1)n)+1]/(5n+6) .

    The parentheses are important.

    What you wrote literally means: [itex]k_n=\frac{(1+(-1)^n)+1}{5n}+6\,,[/itex] which is how uart likely interpreted it.

    There are many numbers between 1/100 and 39/100 which don't have a denominator of 100.

    How many terms of the sequence are between 0.01 and 0.39 ?

    The terms of the sequence with n odd look much different from the terms with n even.
     
  7. Oct 7, 2011 #6
    There are many numbers between 1/100 and 39/100 which don't have a denominator of 100.

    [/QUOTE]
    yeah but i was trying to first find that n for which i shall get the limiting values;i mean 0.01 and 0.39. And i did not understand what you said in the second part
     
  8. Oct 7, 2011 #7

    SammyS

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    If n is odd, (-1)n = -1 .

    If n is even, (-1)n = 1 .
     
  9. Oct 8, 2011 #8
    yeah right i also got till there but what when n is in decimal??
     
  10. Oct 8, 2011 #9

    SammyS

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    n is a positive integer.

    It's a sequence we're talking about.
     
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