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How many liters each of a 25% acid solution and a 70% acid solution must be used to produce 90 liters of a 40% acid solution?
(Round to two decimal places if necessary.)
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x + y = 90, (1) (volume balance, in liters)
0.25x + 0.7y = 0.4*90 (2) (pure acid volume balance, in liters)
From (1), express y = 90 - x and substitute it into equation (2). You will get
0.25x + 0.7*(90 - x) = 36.
Simplify and solve for x:
0.25x + 63 - 0.7x = 36,
-0.45x = 36 - 63,
-0.45x = -27,
x = = 60.
Answer. 60 liters of the 25% acid solution and 90-60 = 30 liters of the 70% acid solution.