Question

The average height of a class of 30 students is 166 cm. The average height of the girls in the class is 158 cm and the average height of the boys is 170 cm. Find the number of boys in the class.

Answer 1

Answer:

Step-by-step explanation:

Let the number of boys be x.Average of total number of student  

=>170x + 158*(30-x) = 166*30

Solving, x = 20

Answer 2

Answer:

Let the number of boys be x

Let the number of girls be y

1st condition,

x + y = 30 ....(I)

The average height of 30 students =Sum of heights of all students/Total number of students=166 cm

The average height of boys =Sum of heights of all boys/total number of boots= 170 cm

The average height of one boy=1/x

The average height of girls = Sum of heights of all girls/total number of girls =158 cm

The average height of one girl=1/y

2nd condition,

1/x +1/y=1/166 .....(II)

from (I)

x=30-y

put the value of x in (II)

1/30-y +1/y=1/166