SOLUTION: 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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Question 1031301: 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.)
Answer by ikleyn(52802) About Me  (Show Source):
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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 = %28-27%29%2F%28-0.45%29 = 60.

Answer. 60 liters of the 25% acid solution and 90-60 = 30 liters of the 70% acid solution.