document.write( "Question 854742: A farmer has 100 gallons of 70% pure disinfectant. He wishes to mix it with disinfectant which is 90% pure to obtain 75% pure disinfectant. How much of the 90% disinfectant must he use? \n" ); document.write( "
Algebra.Com's Answer #514945 by josgarithmetic(39618)\"\" \"About 
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This lesson tells everything necessary for that type of problem:\r
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\n" ); document.write( "\n" ); document.write( "How much to add to a known quantity of known concentration
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