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

$33.3 L$ $33.3"L"$

Amount of substance = concentration x volume

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

$(100 \times 70) + (90 \times V) = 75 (100 + V)$ $(100xx70)+(90xxV)=75(100+V)$

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

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

$:.15V=500$

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