Question 578063
Let {{{ x }}} = ounces of 15% alcohol solution needed
{{{ .2*4 = .8 }}} ounces of alcohol in 20% solution
{{{ .15x }}} = ounces of alcohol in 15% solution
-----------
{{{ ( .15x + .8 ) / ( x + 4 ) = .17 }}}
{{{ .15x + .8 = .17*( x + 4 ) }}}
{{{ .15x + .8 = .17x + .68 }}}
{{{ .02x = .12 }}}
{{{ x = 6 }}}
6 ounces of 15% alcohol solution are needed
check:
{{{ ( .15*6 + .8 ) / ( 6 + 4 ) = .17 }}}
{{{ ( .9 + .8 ) / 10 = .17 }}}
{{{ 1.7/10 = .17 }}}
{{{ 1.7 = 1.7 }}}
OK