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Homework Help: Percentage question

  1. Sep 28, 2010 #1
    1. The problem statement, all variables and given/known data
    So i'm drawing a complete blank on how to figure out some easy math...like given that there is 231 mg of potassium in a dandelion and 93 mg of potassium in lettuce, how much more (%wise) is there of potassium in dandelions....


    2. Relevant equations



    3. The attempt at a solution
    i thought at first that its (93/231)*100= 40.26% but then i started second guessing myself....
     
  2. jcsd
  3. Sep 28, 2010 #2
    (1) How much more is there in dandelion than in lettuce?
    Answer: (amount in dandelion) - (amount in lettuce)
    (2) What percentage is this of the amount of potassium in ....
     
  4. Sep 28, 2010 #3
    sorry but i dont quite get what you said for (2)...
     
  5. Sep 28, 2010 #4
    final-initial/initial = percent gain
     
  6. Sep 28, 2010 #5
    I left the.... to make clear you still had to decide whether you want to know either A or B:

    A: (how much more (%wise) is there of potassium in dandelions than in lettuce) relative to the amount in lettuce.

    B: (how much more (%wise) is there of potassium in dandelions than in lettuce) relative to the amount in dandelion.
     
  7. Sep 28, 2010 #6
    like for some reason, i'm still kind of confused...like this is what i've got...
    (231-93)/93 = 148.39% more potassium in dandelions
    Is this right or should it be the opposite way meaning (231-93)/231= 59.74% more potassium in dandelions....?
     
  8. Sep 28, 2010 #7
    Yes, there is "(231-93)/93 = 148.39% more potassium in dandelions" then in lettuce, relative to the amount in lettuce (that is: the amount more in dandelion than in lettuce is equal to 148.39% of the amount in lettuce)

    When they ask "%-wise" it is not always clear what is meant, a percentage is always relative to something. Another correct answer would be:

    There is (231-93)/231 = 59.74% more potassium in dandelions then in lettuce, relative to the amount in dandelions (that is: the amount more in dandelion than in lettuce is equal to 59.74% of the amount in dandelion)
     
  9. Sep 28, 2010 #8

    Mark44

    Staff: Mentor

    In a way, you're comparing apples to oranges here. The only way you can compare percentages of potassium in dandelions and lettuce is to compare quantities that are comparable. You say there are 231 mg of potassium (K) in a dandelion. How big a serving of lettuce contains the 93 mg of K? Unless otherwise stated you should be comparing one dandelion with an amount of lettuce of about the same weight.
     
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