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linhhhdoi Group Title

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?

  • 2 years ago
  • 2 years ago

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  1. CliffSedge Group Title
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    How many grams of wheat per hectare?

    • 2 years ago
  2. linhhhdoi Group Title
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    3000

    • 2 years ago
  3. CliffSedge Group Title
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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.

    • 2 years ago
  4. CliffSedge Group Title
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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.

    • 2 years ago
  5. linhhhdoi Group Title
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    I'm confused with the first and second step, explain please?

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

    • 2 years ago
  7. CliffSedge Group Title
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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.

    • 2 years ago
  8. linhhhdoi Group Title
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    I got this huge number as the answer "273937.5"

    • 2 years ago
  9. CliffSedge Group Title
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    Good, that should sound reasonable for grams of wheat needed for an entire year.

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

    • 2 years ago
  11. linhhhdoi Group Title
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    What I don't get is where you got "365.25" from?

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

    • 2 years ago
  13. linhhhdoi Group Title
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    Could we use 365 instead of the .25 at the end?

    • 2 years ago
  14. CliffSedge Group Title
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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.

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

    • 2 years ago
  16. linhhhdoi Group Title
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    oh okay, I think i got it. Thanks! :)

    • 2 years ago
  17. CliffSedge Group Title
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    Let me know what you get as your final answer.

    • 2 years ago
  18. linhhhdoi Group Title
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    I got 684375

    • 2 years ago
  19. CliffSedge Group Title
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    Hmmm, what steps did you do after getting 273937.5?

    • 2 years ago
  20. linhhhdoi Group Title
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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

    • 2 years ago
  21. CliffSedge Group Title
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    No, you have to divide the number of kcal by 2.5 kcal/g to get grams

    • 2 years ago
  22. CliffSedge Group Title
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    See how the 2.5 kcal were in the denominator to cancel it with the kcal on top?

    • 2 years ago
  23. CliffSedge Group Title
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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.

    • 2 years ago
  24. linhhhdoi Group Title
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    soo 109500?

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

    • 2 years ago
  26. linhhhdoi Group Title
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    Umm, is it kg of wheat per hectare?

    • 2 years ago
  27. CliffSedge Group Title
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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.

    • 2 years ago
  28. linhhhdoi Group Title
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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.

    • 2 years ago
  29. CliffSedge Group Title
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    What is 'APES?'

    • 2 years ago
  30. linhhhdoi Group Title
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    AP Environmental Science

    • 2 years ago
  31. CliffSedge Group Title
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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.

    • 2 years ago
  32. linhhhdoi Group Title
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    Yeah.. Well that just tells you how bad I am at math in general.

    • 2 years ago
  33. CliffSedge Group Title
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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.

    • 2 years ago
  34. CliffSedge Group Title
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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).

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

    • 2 years ago
  36. CliffSedge Group Title
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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.

    • 2 years ago
  37. linhhhdoi Group Title
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    I got 109.5

    • 2 years ago
  38. CliffSedge Group Title
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    109.5 what? What are the units?

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

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

    • 2 years ago
  41. CliffSedge Group Title
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    I think that should be the right answer. Interesting number, aye? What would it be per day?

    • 2 years ago
  42. linhhhdoi Group Title
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    uhh, is it 13.3225 per day?

    • 2 years ago
  43. CliffSedge Group Title
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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.

    • 2 years ago
  44. linhhhdoi Group Title
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    OHHH.. so 1e-4?

    • 2 years ago
  45. CliffSedge Group Title
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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.

    • 2 years ago
  46. CliffSedge Group Title
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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).

    • 2 years ago
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