Question 861362: In a certain class there are 12 boys and 18 girls, if the average of class for an algebra exam is 90 and the boys average score is 87, what is the girls average score.
Answer by veerajgrewal(1)   (Show Source):
You can put this solution on YOUR website! Given : Number of Boys= 12, Number of girls = 18
Average Marks of class = 90, Average marks of boys = 87
As we know that Average = (Sum of observations)/(Number of observations)
Now, (Total Marks)/(Total Students) = Avg marks of class
(Total Marks)/(12 + 18) = 90
Total Marks = 90*30 = 2700
Now, (Total Marks of boys)/(Number of Boys)= 87
(Total Marks of boys)/12= 87
Total Marks of Boys= 87*12
therefore, Marks of Boys = 1044
Now we know , Total Marks of class = Total Marks of Boys + Total Marks of Girls
Total marks of girls = Total Marks of class - Total Marks of Boys
Total marks of girls = 2700-1044 = 1656
Now Average of girls marks = (Total marks of girls)/(Number of girls)
= 1656/ 18
= 92
The answer is 92.
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