Question 1128170
Let {{{ x }}} = number of small frames she bought
{{{ 20 - x }}} = number of large frames
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{{{ 13*( 20 - x ) + 7x = 170 }}}
{{{ 260 - 13x + 7x = 170 }}}
{{{ -13x + 7x = -90 }}}
{{{ 6x = 90 }}}
{{{ x = 15 }}}
and
{{{ 20 - x = 5 }}}
She bought 15 small and 5 large frames
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{{{ 13*5 + 7*15 = 170 }}}
{{{ 65 + 105 = 170 }}}
{{{ 170 = 170 }}}
OK