Question 276407
.
How many kgs of salt must be added to 24 kg of 20% salt solution in order to increase 
the concentration of salt to 40%?
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        When the problems are talking about salt solutions of high concentration, it is useful to remember

        that water solutions of NaCl can not have concentration higher than 27%.


        At 27%, the solution becomes saturated, and concentration can not go higher than this value.


        This is a standard fact, which students learn from the Science course in their 6-th grade. 



        The second reason why I write these lines, is that the calculations in the post by @mananth 

        are incorrect and inaccurate and lead to wrong answer.


        I came to bring a correct solution.



<pre>
The balance equation for this problem is

    x + 0.2*24 = 0.4*(x+24),

where 'x' is the salt mass to add.


Simplify and find 'x'

    x + 4.8 = 0.4x + 9.6,

    x - 0.4x = 9.6 - 4.8,

      0.6x   =     4.8

         x   =     4.8/0.6 = 8.


<U>ANSWER</U>.  8 kilograms of salt should be added.
</pre>

Solved correctly and explained about the saturation limit.