Question 772436
The lesson here is that you can't get an average
by taking the average of 2 averages. You must 
use the formula:
Average = ( sum of all the scores ) / ( total number of students )
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Use the formula:
Average = ( sum of scores ) / ( number of students )
Sum of scores = ( Average )*( number of students )
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1st sum of scores = 
{{{ .8*35  = 28 }}}
2nd sum of scores:
{{{ .7*15 = 10.5 }}}
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Number of students is {{{ 35 + 15 = 50 }}}
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Average = ( sum of all the scores ) / ( total number of students )
Average = {{{ ( 28 + 10.5 ) / 50 }}}
Average = {{{ 38.5/50 = .77 }}}
The average for the 50 students is 77%