Question 1158509
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Overall average = 0.15*(80+78+92+84) + 0.20*(84) + 0.20*(88) = ________

You can complete the calculation.

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Since the weights don't necessarily need to add to 1 for every weighted average problem, here is the general way to solve this, with step-by-step workout:

Overall average = 
  {{{ (0.15*80 + 0.15*78 + 0.15*92 + 0.15*84 + 0.20*84 + 0.20*88)/(0.15 + 0.15 + 0.15 + 0.15 + 0.20 + 0.20) }}}

= {{{ (0.15*(80+78+92+84) + 0.20*84 + 0.20*88) / (1) }}}   <<< denom=1 for THIS problem

= {{{ 0.15*(80+78+92+84) + 0.20*84 + 0.20*88 }}} = 84.5