A farmer has 100 gallons of 70% pure disinfectant. He wishes to mix it with the disinfectant which is 90% pure to obtain 75% pure disinfectant. How much of the 90% disinfectant must he use?

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Answer 1 · 2016-04-05T11:56:09

#33.3"L"#

Amount of substance = concentration x volume

If #V# is the volume of the 90% disinfectant then we can set up this equation:

#(100xx70)+(90xxV)=75(100+V)#

#:.7000+90V=7500+75V#

#:.90V-75V=7500-7000#

#:.15V=500#

#:.V=500/15=33.33"L"#