THE MEAN WEIGHT OF 150 STUDENTS IN A CLASS IS 60 KG.THE MEAN WEIGHT OF BOYS IN THE CLASS IS 70 KG AND THAT OF GIRLS IS 55 KGS.FIND THE NUMBER OF GIRLS IN THE CLASS.

I hope you find my answer correct....

Let the number of boys be = x
Let the number of girls be = y
total students in the class = 150
Therefore ,
x + y = 150 ----------(1)
Now 
mean weight of boys(x̄​1)  = 70
mean weight of girls(x̄2)= 55
Combined mean weight of 150 students(x̄c) = 60
therefore , by combined arithmetic mean method, we get, 
​1× x + x̄​2× y / 150 = 60
1x +x̄2y = 60 ---------(2)
Solving equations (1) and (2) we get,
x = 50 and y = 100
now number of girls are = y = 100​
 

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