Question 698154
Let {{{ a }}} = gallons of 80% solution needed
{{{ .8a }}} = gallons of acid in 80% solution
{{{ .13*40 = 5.2 }}} gallons of acid in 13% solution
---------------
{{{ ( .8a + 5.2 ) / ( a + 40 ) = .7 }}}
{{{ .8a + 5.2 = .7*( a + 40 ) }}}
{{{ .8a + 5.2 = .7a + 28 }}}
{{{ .1a = 22.8 }}}
{{{ a = 228 }}}
228 gallons of 80% acid solution must be added
check the answer:
{{{ ( .8a + 5.2 ) / ( a + 40 ) = .7 }}}
{{{ ( .8*228 + 5.2 ) / ( 228 + 40 ) = .7 }}}
{{{ ( 182.4 + 5.2 ) / 268 = .7 }}}
{{{ 187.6 / 268 = .7 }}}
{{{ 187.6 = .7*268 }}}
{{{ 187.6 = 187.6 }}}
OK