SOLUTION: the mean weight of 150 students in a certain class is 30kg. the mean weight of the boys in the class is 40kg and the girls is 25kg.Find the number of the boys and girls in the clas

Algebra ->  Probability-and-statistics -> SOLUTION: the mean weight of 150 students in a certain class is 30kg. the mean weight of the boys in the class is 40kg and the girls is 25kg.Find the number of the boys and girls in the clas      Log On


   

Question 839594: the mean weight of 150 students in a certain class is 30kg. the mean weight of the boys in the class is 40kg and the girls is 25kg.Find the number of the boys and girls in the class
Answer by LinnW(1048) About Me  (Show Source):
You can put this solution on YOUR website!
Total weight of class = 150*30 = 4500
Set b = number of boys
g = number of girls
40b + 25g = 4500 , 40kg x number of boys + 25kg x number of girs
also
30b + 30g = 4500
Since each left side = 4500,
30b + 30g = 40b + 25g
add -30b to each side
30g = 10b + 25g
add -25g to each side
5g = 10b
g = 2b
substitute 2b for g in 30b + 30g = 4500
30b +30(2b) = 4500
30b + 60b = 4500
90b = 4500
divide each side by 90
b = 50
since g = 2b,
g = 100