Question 815211
Let {{{ x }}} = your score on the next test
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In order to have an 85 average, you need at least:
{{{ 85 = ( 83 + 87 + x ) / 3 }}}
{{{ 255 = 83 + 87 + x }}}
{{{ x + 170 = 255 }}}
{{{ x = 85 }}}
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In order to have an 90 average, you need at least:
{{{ 90 = ( 83 + 87 + x ) / 3 }}}
{{{ 270 = 83 + 87 + x }}}
{{{ x + 170 = 270 }}}
{{{ x = 100 }}}
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You need to score between 85 and 100 inclusive