Question 1027761
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How many liters of a 40% salt solutions must be added to a 4 liters of a 10% salt solutions to obtain 30% salt solutions?
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Let x be the required amount (volume) of a 40% salt solution.

Then the equation for the pure acid volume is 

0.4x + 0.1*4 = 0.3*(x + 4).

Simplify and solve:

0.4x + 0.4 = 0.3x + 1.2,

0.4x - 0.3x = 1.2 - 0.4,

0.1x = 0.8,

x = {{{0.8/0.1}}} = 8.

<U>Answer</U>. 8 liters of 40% salt solution is needed.
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