Question 1031498
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How many liters each of a 35% acid solution and a 85% acid solution must be used to produce 50 liters of a 55% acid solution?  
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Let x be the required volume of a 35% acid solution, in liters.

Then the volume of a 85% acid solution is (50-x)

The equation for the pure acid volume is 

0.35x + 0.85*(50-x) = 0.55*50.

Simplify and solve:

0.35x + 42.5 - 0.85x = 27.5,

-0.5x = 27.5 - 42.5,

-0.5x = -15,

x = {{{(-15)/(-0.5)}}} = 30.

<U>Answer</U>. 30 liters of the 35% acid solution and (50-30) = 20 liters of the 85% acid solution is needed.
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