Question

the mean weight of 150 students In a class is 60 kg.the mean weight of boys is 70kg. while girls is 50kg.Find the no.of boys and girls in a class

Answer 1

Known:
Σxb=70 kg
Σxg=50 kg
Σx=60 kg
nx=150

So ,nb and ng ?
Use linear equations:
nb.xb+ng.xg=Σx
       nx
70nb+50ng=60
      150
70nb+50ng=9000 ......(1)

and,
nb+ng=150...............(2)

So,
70nb+50ng=9000 | x 1| ⇒70nb+50ng=9000
 nb   +   ng  =150   |x50| ⇒50nb+50ng=7500-
                                                20nb      =1500
                                                    nb       =1500
                                                                   20
                                                                =75 students
And,
nb+ng=150
       ng=150-nb
            =150-75
            =75 students





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