Question 676581
given:
{{{ c/d = 4/7 }}}
{{{ c + d = 440 }}}
---------------
{{{ d = 440 - c }}}
By substitution:
{{{ c / ( 440 - c ) = 4/7 }}}
Multiply both sides by {{{ 7*( 440 - c ) }}}
{{{ 7c = 4*( 440 - c ) }}}
{{{ 7c = 1760 - 4c }}}
{{{ 11c = 1760 }}}
{{{ c = 160 }}}
and
{{{ d = 440 - c }}}
{{{ d = 440 - 160 }}}
{{{ d = 280 }}}
check:
{{{ 160/280 = 4/7 }}}
{{{ 4/7 = 4/7 }}}
OK

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