(May 2014) here is a solution from some seventhgraders in Oregon:

We are a seventh grade class from Timber Ridge School in Albany, Oregon.
In the house there are 6 people, who drink 8 cups a week. Then one Sunday, there are 3 extra people, who drink 1 cup each.
First we multiplied 6 x 8 which is 48, then we added 3, which is 51 cups total.
Based on a 300 ml serving size,they drink 15,300 ml per week. 15,300 ml is about 11 liters. For two weeks, they need about 22 cans of orange juice.

eeps comments:
Notice how different this is from the Swansea solution, below.
Not only are the answers different, but the solutions are as well: they took a different approach.
Which do you prefer?
What account for the differences? Or are they close enough (22 cans vs. 18) that it's just due to assumptions they make? What assumptions?
(One problem is a mistake in wording that looks like a mistake in the math. But it isn't.
The writer used a wrong word, and didn't fully explain what he or she was doing, so a reader can get confused.
This helps show how important it is to write clearly when presenting your work!)

Here's a solution from a group of 7th graders in Swansea, MA:

Question. How many cans of orange juice can last them two weeks?
DAY OF THE WEEK  AMOUNT (mL) PER PERSON  NUMBER OF PEOPLE  PER DAY 
SUNDAY  250  9  2250 
MONDAY  250  6  1500 
TUESDAY  250  6  1500 
WEDNESDAY  250  6  1500 
THURSDAY  250  6  1500 
FRIDAY  250  6  1500 
SATURDAY  500  6  3000 
The Trans family needs to buy 12,750 ml of frozen orange juice to last them one week.
The Trans family needs to buy 25,500 ml of frozen orange juice to last them two weeks.
Since each can makes 1420 mL of juice, we divided 25,500 by 1420 to find out how many cans: 17.957746
But since you can't buy a fraction of a can, we rounded to 18 cans.
By: Justin & Donald
Grade 7 students
Joseph Case Junior High
Swansea, MA

eeps comments:
Hooray! The first solution for this problem!
So, readers, what do you think? That's a huge number of milliliters. Can that be correct? Did the students make the right calculations? 
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