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linhhhdoi

Wheat contains about 2.5 kcal per gram, and the average U.S. male consumes 2500 kcal per day. How many hectares of wheat are needed to support one average U.S. male for a year, assuming that 30 percent of his caloric intake is from wheat?

  • one year ago
  • one year ago

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  1. CliffSedge
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    How many grams of wheat per hectare?

    • one year ago
  2. linhhhdoi
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    3000

    • one year ago
  3. CliffSedge
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    Ok, you can start by multiplying 2500 kcal/day by 365.25 days/year by 30/100 to get kcal per year from wheat.

    • one year ago
  4. CliffSedge
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    Divide that by 2.5 kcal/g to get grams of wheat. Then divide that by 3000 grams/hectare to get the number of hectares.

    • one year ago
  5. linhhhdoi
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    I'm confused with the first and second step, explain please?

    • one year ago
  6. CliffSedge
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    Kilocalories per year from wheat = \[\large 2500 \frac{kcal}{\cancel{day}} \times 365.25 \frac{\cancel{day}}{year} \times \frac{30}{100}\]

    • one year ago
  7. CliffSedge
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    We're ultimately trying to get the number in units of hectares per year, so I need all the other units to cancel out.

    • one year ago
  8. linhhhdoi
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    I got this huge number as the answer "273937.5"

    • one year ago
  9. CliffSedge
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    Good, that should sound reasonable for grams of wheat needed for an entire year.

    • one year ago
  10. CliffSedge
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    Kilocalories per year from wheat divided by 2.5 kcal/g = grams of wheat. \[\large 273937.5 \frac{\cancel{kcal}}{year} \times \frac{grams-of-wheat}{2.5 \cancel{kcal}}\]

    • one year ago
  11. linhhhdoi
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    What I don't get is where you got "365.25" from?

    • one year ago
  12. CliffSedge
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    365.25 = average number of days in a year (to account for possible leap-years).

    • one year ago
  13. linhhhdoi
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    Could we use 365 instead of the .25 at the end?

    • one year ago
  14. CliffSedge
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    Sure, it didn't specify whether it was for a leap-year or not, so you may choose to have your answer for a normal year.

    • one year ago
  15. CliffSedge
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    The precision of these numbers is pretty low anyway, so leaving off the .25 shouldn't make a difference.

    • one year ago
  16. linhhhdoi
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    oh okay, I think i got it. Thanks! :)

    • one year ago
  17. CliffSedge
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    Let me know what you get as your final answer.

    • one year ago
  18. linhhhdoi
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    I got 684375

    • one year ago
  19. CliffSedge
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    Hmmm, what steps did you do after getting 273937.5?

    • one year ago
  20. linhhhdoi
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    I went back and changed the number of days in year to 365. therefore i times that by 2.5 and got 684375

    • one year ago
  21. CliffSedge
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    No, you have to divide the number of kcal by 2.5 kcal/g to get grams

    • one year ago
  22. CliffSedge
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    See how the 2.5 kcal were in the denominator to cancel it with the kcal on top?

    • one year ago
  23. CliffSedge
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    This is why you have to include units in your calculations to see whether to multiply or divide to cancel out the units you don't want.

    • one year ago
  24. linhhhdoi
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    soo 109500?

    • one year ago
  25. CliffSedge
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    Right, now what's the next step? What are the units of that number, 109500? That will guide you.

    • one year ago
  26. linhhhdoi
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    Umm, is it kg of wheat per hectare?

    • one year ago
  27. CliffSedge
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    Dividing kcal/year by kcal/g = grams/year. Why did you say kg? I'm curious. .. . Are you sure its 3000 grams per hectare and not 3000 kg per hectare? 3000 grams per hectare seems kinda small.

    • one year ago
  28. linhhhdoi
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    Haha, I'm very sorry. I'm not learning in APES at all so I'm just straight up dumb at this subject.

    • one year ago
  29. CliffSedge
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    What is 'APES?'

    • one year ago
  30. linhhhdoi
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    AP Environmental Science

    • one year ago
  31. CliffSedge
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    Ah, well, I hate to be the bearer of bad news, but this unit conversion stuff is the easy part of the course.

    • one year ago
  32. linhhhdoi
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    Yeah.. Well that just tells you how bad I am at math in general.

    • one year ago
  33. CliffSedge
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    This can be a tricky topic for people, but that's why I stress always including the unit with the number and always thinking, "how do I make the units I don't want cancel out leaving me only the units I do want?" If you write it out and cancel the units like I have been showing you, it practically solves itself.

    • one year ago
  34. CliffSedge
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    So, do we have a confirmation of whether a hectare is 3000 grams of wheat, or is it 3000 kilograms? (It makes a big difference).

    • one year ago
  35. linhhhdoi
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    Dude, you're awesome. I will use your tip. Thanks a bunch! It says 3000 kg of wheat per hectare

    • one year ago
  36. CliffSedge
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    Ok, so the 109500 number is in grams per year. Divide that by 1000 g/kg to get the number in kg.

    • one year ago
  37. linhhhdoi
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    I got 109.5

    • one year ago
  38. CliffSedge
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    109.5 what? What are the units?

    • one year ago
  39. CliffSedge
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    The units should be kg/year. Divide by 3000 kg/hectare to get hectares per year.

    • one year ago
  40. linhhhdoi
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    So divide 109.5 by 3000 and I will get .0365 kg/hectare per year?

    • one year ago
  41. CliffSedge
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    I think that should be the right answer. Interesting number, aye? What would it be per day?

    • one year ago
  42. linhhhdoi
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    uhh, is it 13.3225 per day?

    • one year ago
  43. CliffSedge
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    If it is 0.0365 kg/hectare per year and a year has 365 days, then you divide by 365 days per year to get the number per day. Also note that a hectare = 100 acres.

    • one year ago
  44. linhhhdoi
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    OHHH.. so 1e-4?

    • one year ago
  45. CliffSedge
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    Right, so since there are 100 acres in a hectare, and it takes 0.0001 hectares of wheat per day to feed a dude, that's 0.01 acre of wheat per day to feed the average U.S. male.

    • one year ago
  46. CliffSedge
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    For additional practice in this method, try this simpler example: Convert 55 miles per hour into feet per second. (show your work).

    • one year ago
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