Question 1053659
The fraction of oil to total mixture is:
{{{ 1/51 }}}
{{{ (1/51)*5*128 = 640/51 }}} fl oz of oil
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{{{ ( 640/51 + x ) / ( 640 + x ) = 1/41 }}}
{{{ 640/51 + x = (1/41)*( 640 + x ) }}}
{{{ 640/51 + x = 640/41 + x/41 }}}
Multiply both sides by {{{ 41*51 }}}
{{{ 41*640 + 41*51*x = 51*640 + 51x }}}
{{{ 40*51*x = 10*640 }}}
{{{  2040x = 6400 }}}
{{{ x = 3.13725 }}} fl oz of oil shouyld be added
check:
{{{ 1/40 = ( 12.54902 + 3.13725 ) / ( 640 - 12.54902 - 3.13725 ) }}}
{{{ 1/40 = 15.68627 / 624.31373 }}}
{{{ 1/40 = .02512562 }}}
{{{ 1 = 1.00502 }}}
I expected to be closer
Check my work