There are 50 students in a class, out of which 20 are girls and 30 are boys. The average height of all the girls is 5 ft and the average height of all boys is 6ft. Find the average height of all the students in the class.

Given, the No. of girls in class = 20

The average height of all the girls = 5 ft

∴Sum of heights of all girls in the class 

= Average height No. of girls

= 5ft × 20 

= 100 ft

No. of boys in class = 30

The average height of all the boys 

= 6 ft

∴Sum of heights of all girls in the class

=Average height No. of girls

= 6 ft × 30 

= 180 ft

Now, Sum of heights of all boys and girls 

= 100 ft + 180 ft 

= 280 ft

Total no. of students in class = 50

∴ Average height of all students = $\frac{280}{50} = 5.6 ft$

Thus, the average height of all the students in the class is 5.6 ft.