Question 405382
Let {{{a}}} = liters of 40% solution needed
given:
{{{.2*12 = 2.4}}} liters of acid in 20% solution
{{{.4a}}} = liters of acid in 40% solution
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{{{(.4a + 2.4)/(a + 12) = .25}}}
{{{.4a + 2.4 = .25*(a + 12)}}}
{{{.4a + 2.4 = .25a + 3}}}
{{{.15a = .6}}}
{{{15a = 60}}}
{{{a = 4}}}
4 liters of 40% solution are needed
check answer:
{{{(.4*4 + 2.4)/(4 + 12) = .25}}}
{{{4/16 = .25}}}
{{{.25 = .25}}}
OK