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Homework Help: Substitution Problem

  1. Dec 30, 2009 #1
    1. The problem statement, all variables and given/known data

    d1/d2 + d2/v2 = 0.500km/v1 + 3.50km/2v1 = 0.250h

    2. Relevant equations

    v2 = 2v1

    3. The attempt at a solution

    The answer is 9.00km/h but I keep coming up with 5.33. I know this is simple algebra but I am missing something in the order of operations.

    0.500km/v1 + 3.50km/2v1 = 0.250h

    4.00km/3v1 = 0.250h

    4.00/(0.250h)(3) = v1

    v1 = 5.33 ??
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Dec 30, 2009 #2
    [tex]\frac{a}{b}+\frac{c}{d}\neq \frac{a+c}{b+d}[/tex]

    At this point:
    [tex]\frac{0.5 km}{v_1}+\frac{3.5 km}{2v_1}=0.25 hr[/tex]

    Multiply both sides by [tex]v_1[/tex] and remember how to add fractions!

    [tex]\frac{a}{b}+\frac{c}{d}= \frac{ad+bc}{bd}[/tex]
  4. Jan 2, 2010 #3
    Thanks again for your help!! I'm new to the forum and still learning to navigate the site. I am taking an online physics course and will be needing your help in the future I'm sure. I'll be in touch.
  5. Jan 2, 2010 #4
    Sure thing man. :) But I suggest you work a bit on your algebra first, since you'll be using it a lot!
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