SOLUTION: A class of 30 students has more girls than boys. On a certain test, the girls averaged 65 marks, while the boys averaged 60 marks. If the average for the whole class if 63, how man

Question 843480: A class of 30 students has more girls than boys. On a certain test, the girls averaged 65 marks, while the boys averaged 60 marks. If the average for the whole class if 63, how many girls are in the class?
Answer by LinnW(1048) (Show Source): You can put this solution on YOUR website!
Set b = no of boys , g = no of girls
Set m = total of marks for the class
g = 30 - b
m = 63*30
m = 1890
m = 65g + 60b
1890 = 65g + 60b
substitute 30 - b for g in above
1890 = 65(30 - b) + 60b
1890 = 1950 -65b + 60b
1890 = 1950 -5b
add -1950 to each side
-60 = -5b
divide each side by -5
12 = b
Since g = 30 - b ,
g = 30 - 12
g = 18
Substitute into 1890 = 65g + 60b to check
1890 =? 65(18) + 60(12)
1890 =? 1170 + 720
1890 = 1890

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