Question 1009979
Let {{{ x }}} = pounds of 60/pound nuts to be added
{{{ 60x }}} = cost of {{{ x }}} pounds of 60/pound nuts
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{{{ ( 60x + 120*100 ) / ( x + 100 ) = 90 }}}
{{{ 60x + 12000 = 90*( x + 100 ) }}}
{{{ 60x + 12000 = 90x + 9000 }}}
{{{ 30x = 3000 }}}
{{{ x = 100 }}}
100 pounds of 60/pound nuts should be added
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check:
{{{ ( 60x + 120*100 ) / ( x + 100 ) = 90 }}}
{{{ ( 60*100 + 120*100 ) / ( 100 + 100 ) = 90 }}}
{{{ ( 6000 + 12000 ) / 200 = 90 }}}
{{{ 18000 / 200 = 90 }}}
{{{ 90 = 90 }}}
OK