Question 861805
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Hi,
{{{n - (1/6)n - (1/2)n = 40}}}
 {{{ n - (4/6)n = 40}}}
   {{{(2/6)n = 40}}}
       {{{n = 40*(6/2)}}} = 120 people attended
$2*20 + $3*40 + $6*60 = $40 + $120 + $360 = $520