Question 354378
How many liters of a 20% acid solution must be mixed with a 60% solution to obtain 40 liters of a 35% 
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Equation:
acid + acid = acid
0.20x + 0.60(40-x) = 0.35*40
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Multiply thru by 100 to get:
20x + 60*40 - 60x = 35*40
-40x = -25*40
x = 25 liters (amt. of 20% solution needed in the mixture)
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Cheers,
Stan H.