Question 571231
Let {{{ x }}} = gallons of 5% solution needed
{{{ .05x }}} = gallons of salt is 5% solution
{{{ .15*63 = 9.45 }}} = gallons of salt in 15% solution
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{{{ ( .05x + 9.45 ) / ( x + 63 ) = .12 }}}
{{{ .05x + 9.45 = .12*( x + 63 ) }}}
{{{ .05x + 9.45 = .12x + 7.56 }}}
{{{ .12x - .05x = 9.45 - 7.56 }}}
{{{ .07x = 1.89 }}}
{{{ x = 27 }}}
27 gallons of 5% solution are needed
check answer:
{{{ ( .05*27 + 9.45 ) / ( 27 + 63 ) = .12 }}}
{{{ ( 1.35 + 9.45 ) / 90 = .12 }}}
{{{ 10.8 = .12*90 }}}
{{{ 10.8 = 10.8 }}}
OK