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Math Help - Simple conversion problem.

  1. #1
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    Angry Simple conversion problem.

    Hi,
    I have this problem that I can't figure out. I've had quite a few attempts, but am really not sure where I'm going wrong. It's a simple question, so I'm sure it's something silly I'm doing...

    Anyway,

    A flash flood left a 200 hectare property ankle deep (100 mm) in water. How much water is this in mega litres? (1 hectare = 100m x 100m. 1 litre = 1000 cm3)

    So, if 1 hectare = 100m2, then 200 hectare = 20,000m2.

    Based on this, to determine the volume of water, we could multiply the area by the height of the water - 100mm, or 0.1m. 20,000m2 * 0.1m = 2,000m3.

    I now have to convert this to litres, and by knowing that 1L = 1cm3, I should convert m3 to cm3. 1 m3 = 1,000,000cm3, so 2,000m3 = 2,000,000,000cm3.

    Now, if 1 L is equal to 1000cm3, then 20,000,000,000cm3 = 2,000,000L.

    Then, if 1 Megalitre = 1,000,000 L, then 2,000,000L = 2 megalitres.

    However, according to the quiz sheet, this is incorrect...Could someone please explain?
    ,



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  2. #2
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    Re: Simple conversion problem.

    1 hectare is 10000 $m^2$ not 100
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  3. #3
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    Re: Simple conversion problem.

    Systematically, and without thinking about it:

    1hct•10000(m2/hct)•100mm•1m/1000mm•1L/1000cm3•(100cm/m)3•1megaL/106L= 1megaL

    ck units: hct•m2/hct•m•L/cm3•cm3/m3•megaL/L=megaL
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  4. #4
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    Re: Simple conversion problem.

    1 Litre is 1 dm3, or 1000 cm3
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    Re: Simple conversion problem.

    Quote Originally Posted by Shakarri View Post
    1 Litre is 1 dm3, or 1000 cm3
    ie, 1L/1000cm3

    1hct•10000(m2/hct)•100mm•1m/1000mm•1L/1000cm3•(100cm/m)3•1megaL/106L= 1megaL

    You missed the point.
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  6. #6
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    Re: Simple conversion problem.

    I was replying to astuart not to you. I can see what you did but without explanation it might not make sense, your "without thinking about it" approach doesn't help much with understanding.
    Last edited by Shakarri; March 13th 2014 at 11:31 AM.
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  7. #7
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    Re: Simple conversion problem.

    The standard procedure for unit conversion is:

    Quote Originally Posted by Hartlw View Post
    Systematically, and without thinking about it:

    1hct•10000(m2/hct)•100mm•1m/1000mm•1L/1000cm3•(100cm/m)3•1megaL/106L= 1megaL

    ck units: hct•m2/hct•m•L/cm3•cm3/m3•megaL/L=megaL
    You can use any units you want as long as they cancel out- it's a mechanical procedure.

    If you have a different way, use it.

    Post #4 was trivial and irrelevant.
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  8. #8
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    Re: Simple conversion problem.

    Post #4 was trivial and irrelevant.
    My post was a follow on from romsek's.
    Your post might not have been clear. You can't seem to see it from the perspective of someone who doesn't understand unit conversion. It looks like gibberish if someone is missing just a bit of understanding of what you are doing. For example, depending on what level of pre-university they are in they might not have used dot notation as multiplication. My opinion was that you took too much pre-requisite knowledge for granted and that it might not be understood so assuming that your post was overlooked because it was confusing he would have romsek's hint and my hint which correct his mistakes allowing him to finish the problem by himself.

    If you have a different way, use it.
    I am here to teach
    Last edited by Shakarri; March 13th 2014 at 12:00 PM.
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  9. #9
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    Re: Simple conversion problem.

    Quote Originally Posted by Shakarri View Post
    1 Litre is 1 dm3, or 1000 cm3
    By definition, i liter is a volume of 10cmX10cmX10cm. or 1L/1000cm3 which astuar used in OP.
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  10. #10
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    Re: Simple conversion problem.

    Ah yes, you are right, he did. I only read where he said "I now have to convert this to litres, and by knowing that 1L = 1cm3"
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  11. #11
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    Re: Simple conversion problem.

    Quote Originally Posted by Shakarri View Post
    I am here to teach
    So teach. How would you solve OP?
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  12. #12
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    Re: Simple conversion problem.

    Quote Originally Posted by Hartlw View Post
    So teach. How would you solve OP?
    I don't solve the problems I help the OP solve the problem by guiding them so that they can make their own realizations and then understand the mathematics on a deeper level.
    Thanks from romsek
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  13. #13
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    Re: Simple conversion problem.

    How about:
    (mi/gal)gal=mi, does that require explanation?
    ex: (5mi/gal)3gal=15mi


    Let’s get “advanced:”
    (mi/gal)(1.609km/mi)(1gal/3.79L)=.434km/L
    1mi/gal=.434km/L
    5mi/gal = 5(.434km/L) = (2.17)km/L, or
    5mi/gal(.434km/L)/(1mi/gal) = (2.17)km/L, or, directly:
    (5mi/gal)(1.609km/mi)(1gal/3.79L)= (2.17)km/L

    I look forward to OP’s solution using your’s and romsek’s guidelines.

    I will admit it's easier to "see" if you can write the terms as a over b instead of a/b.
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    Re: Simple conversion problem.

    Quote Originally Posted by Hartlw View Post
    Systematically, and without thinking about it:

    1hct•10000(m2/hct)•100mm•1m/1000mm•1L/1000cm3•(100cm/m)3•1megaL/106L= 1megaL

    ck units: hct•m2/hct•m•L/cm3•cm3/m3•megaL/L=megaL
    Good grief! It's 200hct, not 1hct. So the ans is 200ML.

    You could have nailed me on that.
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  15. #15
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    Re: Simple conversion problem.

    Quote Originally Posted by Hartlw View Post
    Good grief! It's 200hct, not 1hct. So the ans is 200ML.

    You could have nailed me on that.
    You see, that's the difference here. We're not here to "nail" anyone.
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