SOLUTION: 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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Question 1027761: 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?
Answer by ikleyn(52788) About Me  (Show Source):
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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%2F0.1 = 8.

Answer. 8 liters of 40% salt solution is needed.