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linhhhdoi
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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
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

This Question is Closed

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
How many grams of wheat per hectare?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
I'm confused with the first and second step, explain please?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
I got this huge number as the answer "273937.5"
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Good, that should sound reasonable for grams of wheat needed for an entire year.
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Kilocalories per year from wheat divided by 2.5 kcal/g = grams of wheat. \[\large 273937.5 \frac{\cancel{kcal}}{year} \times \frac{gramsofwheat}{2.5 \cancel{kcal}}\]
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
What I don't get is where you got "365.25" from?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
365.25 = average number of days in a year (to account for possible leapyears).
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
Could we use 365 instead of the .25 at the end?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Sure, it didn't specify whether it was for a leapyear or not, so you may choose to have your answer for a normal year.
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
The precision of these numbers is pretty low anyway, so leaving off the .25 shouldn't make a difference.
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
oh okay, I think i got it. Thanks! :)
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Let me know what you get as your final answer.
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
I got 684375
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Hmmm, what steps did you do after getting 273937.5?
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
No, you have to divide the number of kcal by 2.5 kcal/g to get grams
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
See how the 2.5 kcal were in the denominator to cancel it with the kcal on top?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
soo 109500?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
Right, now what's the next step? What are the units of that number, 109500? That will guide you.
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
Umm, is it kg of wheat per hectare?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
What is 'APES?'
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
AP Environmental Science
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
Yeah.. Well that just tells you how bad I am at math in general.
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
Dude, you're awesome. I will use your tip. Thanks a bunch! It says 3000 kg of wheat per hectare
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
I got 109.5
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
109.5 what? What are the units?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
The units should be kg/year. Divide by 3000 kg/hectare to get hectares per year.
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
So divide 109.5 by 3000 and I will get .0365 kg/hectare per year?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
I think that should be the right answer. Interesting number, aye? What would it be per day?
 2 years ago

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
uhh, is it 13.3225 per day?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

linhhhdoi Group TitleBest ResponseYou've already chosen the best response.0
OHHH.. so 1e4?
 2 years ago

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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

CliffSedge Group TitleBest ResponseYou've already chosen the best response.1
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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