Question 749867
Pounds of cement in 50% mix = {{{ .5*14 = 7 }}}
Let {{{ x }}} = pounds of 80% mix needed
{{{ .8x }}} = pounds of cement in 80% mix
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{{{ ( 7 + .8x ) / ( 14 + x ) = .6 }}}
{{{ 7 + .8x = .6*( 14 + x ) }}}
{{{ 7 + .8x = 8.4  + .6x }}}
{{{ .2x = 1.4 }}}
{{{ x = 7 }}}
7 pounds of 80% mix are needed
check:
{{{ ( 7 + .8x ) / ( 14 + x ) = .6 }}}
{{{ ( 7 + .8*7 ) / ( 14 + 7 ) = .6 }}}
{{{ 12.6 / 21 = .6 }}}
{{{ 12.6 = .6*21 }}}
{{{ 12.6 = 12.6 }}}
OK