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Math Help - Question

  1. #1
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    Question

    Three numbers p, q and r are all prime numbers less than 50 with the property that  p+q=r . How many values of r are possible?

    I would think this is 0 because prime numbers have to be odd and odd + odd always equals an even number. But the answer is not 0
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  2. #2
    Member SENTINEL4's Avatar
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    It's not all prime numbers odd. You forget 2 which is prime and even.
    Then if p=2 and q=3 then p+q=2+3=5=r and p,q,r are all primes.
    Same if p=2 and q=5 then r=7.
    Check if there are any more...
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  3. #3
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    wow forgot about 2...

    ok

    2,3
    2,5
    2,11
    2,17
    2,29
    2,41

    did i miss any?
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  4. #4
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    OK I have another one.

    When 1000^2008 is written as a numeral, the number of digits written is..

    How do you go about doing this?
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  5. #5
    Member SENTINEL4's Avatar
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    I don't quite understand what you want for the last one you asked 1000^{2008}
    You want to know how many digits this number has?? Too many!
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  6. #6
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    1000^1 = 1000 ( 4 digits)

    1000^2 = 1,000,000 (7 digits)

    1000^3 = 1,000,000,000 (10 digits)

    there is pattern ^^
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  7. #7
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    oo alright! so if  1000^2 has 7 digits (6 zeros) that means

    2008\div2 = 1004

     1004* 6 = 6024 + 1 (the extra 1) is 6025!
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