Question 345458
Let {{{x}}} = liters of pure acid needed
In words:
(total liters of acid)/(total liters of solution) = 20%
given:
acid already in solution: {{{.15*20 = 3}}} liters
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{{{(x + 3)/(20 + x) = .2}}}
{{{x + 3 = 4 + .2x}}}
{{{.8x = 1}}}
{{{x = 1.25}}} liters
1.25 liters of acid are needed
check:
{{{(x + 3)/(20 + x) = .2}}}
{{{(1.25 + 3)/(20 + 1.25) = .2}}}
{{{4.25/21.25 = .2}}}
{{{4.25 = .2*21.25}}}
{{{4.25 = 4.25}}}
OK