Question

There are 100 students in class the mean height of the class is 150 cm if the height of 60 boys is 170 cm find the mean height of girls in the class

Answer 1

Sum of observations/ number of observations =mean
1)total students=100
Number of boys =60
Number of girls=40
2) mean height of 100 students=150
Sum of heights of the 100 students=150000----(1)
3) mean. Height of 60 boys =170
Sum of heights of 60 boys =170×60=10200----(2)
Sum of the heights of 40 girls =(1) -(2)
=15000-10200
=4800
Mean height of 40 girls = 4800/40
=120

Answer 2

Total students in the school=100
Mean height of students of the school=150

Mean=sum of observation/No of observation


Height of each boy in the class =170 cm
Sum of height of all the boys=170×60=10200cm
Mean height of boys=10200/60=170cm

Similarly,
Let the sum of height of all the girls be X
Mean height of girls=X/40           [100-60(boys)]

According to the question:
Mean height of boys and girls (Total students in the school)=150cm

∴[10200(sum of boys height)+x(sum of girls height)]/100=150

(10200+x)/100=150
10200+x=15000
x=4800

Mean height=4800/40=120 cm

∴120cm is the mean height of the girls.