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Unit Conversions

Date: 11/15/97 at 19:54:31
From: Jenna
Subject: Unit conversions

How many cups are in 4 liters?

Date: 11/15/97 at 20:47:02
From: Doctor Guy
Subject: Re: Unit conversions

The answer to this question depends on how precise you want to be. 
The difficulty is that liters and cups are in two different 
measurement systems, and it is not very easy to convert between them.

If you want this answer only very roughly, you can say that a liter 
is a little bit more than a quart, so 4 liters is a bit more than 
4 quarts. Then each quart is 2 pints, and each pint is 2 cups, so 
4 liters is a bit more than 16 cups, say about 17 cups.

However, if you want more accuracy than this, we will have to look up 
the equivalents somewhere, say on a soda bottle. I have a bottle of 
raspberry seltzer water that says that it has 20 fluid ounces, and 
that is equivalent to 591 milliliters. There are 8 fluid ounces in a 
cup, so this bottle has 2-and-a-half cups, or 2.5 cups. 

591 milliliters is 0.591 liters, because there are 1000 milliliters 
(or ml, or cc, which means cubic centimeters) in one liter.

I can then set up a proportion, using the information I found from 
this bottle:

0.591 liters / 2.5 cups = 4 liters / c cups

which I can also write this way:

0.591      4
_____  =  ____
 2.5       c

To solve this, algebra books tell you that when two fractions are 
equal, then the cross-products must also be equal. Therefore, 0.591 
times c equals 4 times 2.5, or 0.591c = 10.0 .

Then I use a calculator to divide both sides by 0.591, and I get 
that c is approximately 16.92 cups, which was about what I said in the 
first place.

-Doctor Guy,  The Math Forum
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Associated Topics:
Middle School Terms/Units of Measurement

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