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What does this sentence mean?

  1. Sep 3, 2010 #1
    This isn't even my homework, but I'm disagreeing on a friend on what it's asking.
    Dunno what forum to ask it in lol, sorry.

    "Using only different combinations of those variables and the addition and subtraction operators, print all the positive weights that can be measured with 9, 3, and 1 pound measures (1-13). "

    Do you think it means necessarily use all 3, or can you just pick (for example) one of the weights by itself and count that as a combination?

    (don't need help doing the actual question, whichever it turns out to be)
     
  2. jcsd
  3. Sep 3, 2010 #2

    cronxeh

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    I think it just means 9x + 3y + z, 9x-3y-z, 9x-3y+z, 9x+3y-z, z-9x-3y, 3y-9x-z, etc where x,y,z are any positive integers. Since it says combinations I guess you need to use at least 2, but using all 3 is obviously the most optimal combination given the set

    Or does it mean only 9 +/- 3 +/- 1 ?? Seriously, who teaches English to these math book writers
     
    Last edited: Sep 3, 2010
  4. Sep 3, 2010 #3
    "(1-13)" is a big hint, i think
     
  5. Sep 3, 2010 #4
    Good point, Proton Soup.
    But it's hard to say for sure if the 1 is like...precisely "inclusive".

    Also I think only one of each weight can be used.

    Also, a good mathematician would make it clear >:
    (using the most dull and possibly repetitive language possible)
     
  6. Sep 3, 2010 #5

    cronxeh

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    Ok so 9-3-1 is only 5lbs.

    9+3+1 is 13 pounds. So you can't use all 3 to get minimum weight.

    What was the point of this exercise?
     
  7. Sep 3, 2010 #6
    9+3+1
    9+3-1
    9-3+1
    9-3-1

    Think thats all of them. Is this really a math problem? Christ no wonder our public school fails this is a friggin word game. I'm assuming the 9, 3, and the 1 are the "variables", unless you skipped a part of the question?
     
  8. Sep 3, 2010 #7
    enumeration?
     
  9. Sep 3, 2010 #8

    cronxeh

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    The wha?

    Thats like 'find x. There it is! ---> x'


    You give me 1, 3, and 9 and ask me to find (1-13). And I must say.. THERE IS 1!! Oh wait it gets better. 1+3 = 13!
     
  10. Sep 3, 2010 #9
    i don't think that's what it's asking.

    1 = 1
    2 = 3-1
    3 = 3
    4 = 3+1
    5 = 9-3-1
    6 = 9-3
    7 = 9-3+1
    8 = 9-1
    9 = 9
    10 = 9+1
    11 = 9+3-1
    12 = 9+3
    13 = 9+3+1

    so, with those three values, you can represent every integer weight between 1 and 13
     
  11. Sep 3, 2010 #10
    actually, i think a lot of graph theory proofs are solved by enumeration. not very proofy, but proof is proof.
     
  12. Sep 3, 2010 #11

    cristo

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    I think the question means you can use any combination of the 9lb, 3lb and 1lb measure (including not using one or two of them).
     
  13. Sep 7, 2010 #12
    I think it means that too.

    Btw, it was a programming exercise. So it's "Write a program that ___".
     
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