Question 400731
Let add x liters of a 14% alcohol solution to 20L of a 50% solution, then will have {{{(x+20)}}}liters of a 30% solution 
In x liters of a 14% alcohol solution is {{{0.14x}}} liters of alcohol
In 20 liters of a 50% alcohol solution is {{{0.5*20=10}}} liters of alcohol
In {{{(x+20)}}} liters of a 30% alcohol solution is {{{0.3*(x+20)}}} liters of alcohol
equation
{{{0.14x+10=0.3*(x+20)}}}
{{{0.14x+10=0.3x+6}}}
{{{0.14x-0.3x=6-10}}}
{{{-0.16x=-4}}}
{{{x=(-4)/(-0.16)}}}
{{{x=25}}}liters of a 14% alcohol solution must be mixed with 20L of a 50% solution to get a 30% solution