Question 1011330
Let {{{ x }}} = number of questions she got right
{{{ 20 - x }}} = number she got incorrect
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{{{ 2x - 1*( 20 - x ) = 19 }}}
{{{ 2x - 20 + x = 19 }}}
{{{ 3x = 39 }}}
{{{ x = 13 }}}
She got 13 questions right
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check:
{{{ 2x - 1*( 20 - x ) = 19 }}}
{{{ 2*13 - 1*( 20 - 13 ) = 19 }}} 
{{{ 26 - 20 + 13 = 19 }}}
{{{ 39 - 20 = 19 }}}
{{{ 19 = 19 }}}
OK