Question 414986
Let {{{x}}} = quarts of pure antifreeze needed
{{{.2*4 = .8}}} = pure antifreeze in 20% solution
{{{ (x + .8) / (x + 4) = .5}}}
{{{ x + .8 = .5*(x + 4) }}}
{{{x + .8 = .5x + 2}}}
{{{.5x = 1.2}}}
{{{x = 2.4}}}
2.4 quarts of pure antifreeze must be added
check:
{{{ (x + .8) / (x + 4) = .5}}}
{{{ (2.4 + .8) / (2.4 + 4) = .5}}}
{{{3.2/6.4 = .5}}}
{{{3.2 = 3.2}}}
OK