Question 423336
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A liter of orange fruit drink contains 22% orange juice. How many millimeters of orange juice 
must be added to produce a mixture containing 50% orange juice?
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        The solution in the post by @mananth is irrelevant to the given problem,  since it uses 

        numerical values different from the given input data.


        So,  I came to provide an adequate solution.



<pre>
As given, the liter of orange fruit drink contains 22%, or 220 mL of orange juice.

Let assume that we add x milliliters of orange juice.


Then we will have the total volume of 1000 + x milliliters with the (220+x) milliliters 
of orange juice.

The concentration will be  {{{(220+x)/(1000+x)}}}.


We want this concentration be 50%, or 0.5 as a decimal.

So, our equation is

    {{{(220+x)/(1000+x)}}} = 0.5.


Simplify and find x

    220 + x = 0.5 * (1000 + x),

    220 + x = 500 + 0.5x,

    x - 0.5x = 500 - 220,

       0.5x  =    280,

          x  =    280/0.5 = 560.


<U>ANSWER</U>.  560 milliliters of orange juice should be added.
</pre>

Solved correctly.