Question

The weight of 150 students in a class is 60 kg.the mean weight of boys students is 70 kg. And that of girls students is 55 kg. Find the number of boys and girls in the class.

Answer 1

Boys-50
Girls-100
Total no. of students=150
Therefore, number of boys +number of girls =150
Nb+Ng=150 eqn 1
Nb=150-Ng eqn 2
{Boys' weight+girls'weight}/150=60,from the first statement
Therefore, ({boys' weight +{girls' weight)=9000
{boys' weight=70Nb
{Girls'weight=55Ng
Therefore, 70Nb+55Ng=9000 eqn 3
By solving eqn 1 and 3 simultaneously, NB=50 and Ng=100

Answer 2

question must be mean weight of 150 students is 60 kg.

Sol: let no of boy students=b
let no of girl students=g

b+g=150 --------------1

Avg weight of boys = 70kg
( b1+ b2+b3+------+bn )/b =70
b1+ b2+b3+------+bn =70b ---------2



Avg weight of girls = 55kg
( g1+ g2+g3+------+gn )/g =55
( g1+ g2+g3+------+gn ) =55g ---------3

If mean weight is 60 kg then

[ ( b1+ b2+b3+------+bn ) + ( g1+ g2+g3+------+gn ) ] / 150 = 60

from ---2 and ----3
70b+55g=150*60 -----------4

solving ------1 and -------4 we get b and g as

b=50 and g= 100