A group of 100 students took a quiz.

Question

Their average score was 76 points. If the average score for the boys was 80 points and the average score for the girls was70 points, how many girls participated in the quiz? 

Answer 1

b = number of boys

g = number of girls

 

b + g = 100

 

If the average of 100 scores is 76, then the scores added to 7600.

 

80b + 70g = 7600

 

Multiply first equation by 70 and subtract from the second.

 

10b = 600

b = 60

g = 40

 

The class had 60 boys and 40 girls.