Question 631697
Let {{{ a }}} = gallons of pure alcohol needed
{{{ .2*5 = 1 }}} gallons of pure alcohol in 20% solution
given:
{{{ ( a + 1 ) / ( a + 5 ) = .5 }}}
{{{ a + 1 = .5*( a + 5 ) }}}
{{{ a + 1 = .5a + 2.5 }}}
{{{ a - .5a = 2.5 - 1 }}}
{{{ .5a = 1.5 }}}
{{{ a = 3 }}}
3 gallons of pure alcohol are needed
check:
{{{ ( a + 1 ) / ( a + 5 ) = .5 }}}
{{{ ( 3 + 1 ) / ( 3 + 5 ) = .5 }}}
{{{ 4/8 = .5 }}}
{{{ .5 = .5 }}}
OK