SOLUTION: how much of a 25% acid solution must be mixed with 4 gallons of an 18% acid solution to get a 21% acid solution?

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Question 896539: how much of a 25% acid solution must be mixed with 4 gallons of an 18% acid solution to get a 21% acid solution?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
how much of a 25% acid solution must be mixed with 4 gallons of an 18% acid solution to get a 21% acid solution?
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Equation:
acid + acid = acid
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0.25x + 0.18*4 = 0.21(x+4)
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25x + 18*4 = 21x + 21*4
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4x = 3*4
x = 3 gallongs (amt. of 25% solution needed)
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Cheers,
Stan H.
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