Question 1130950
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Let x = the amount of water (in liters), and y = the amount of the 70% acide solution.



First equation is for the total volume of the solution

x + y = 5     liters.     (1)



Second equation is for the final mixture concentration

{{{(0.7y)/5}}} = 0.28     (2)  (concentration is the ratio of the pure acid volume to the total liquid volume)



From equation (2)  you get   y = {{{(0.28*5)/0.7}}} = 2.


Then from equation (1) the rest,  5-2 = 3 liters is the water volume.



<U>Answer</U>.  2 liters of water and 3 liters of the 70% solution to be mixed.


<U>Check</U>.   {{{(0.7*2)/5}}} = 0.28 = 28%.    ! Correct !
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Solved.