The average height of 20 students of Class 9 is 147cm and the average height of $15 students of Class 10 is 154cm. What is the average height (in cm) of the students of the two Classes?

We can use the weighted average formula to find the combined average height of both classes:
Combined Average=
n
1
​
+n
2
​

(n
1
​
×A
1
​
)+(n
2
​
×A
2
​
)
​

Where:

n
1
​
=20 (number of students in Class 9)

A
1
​
=147cm (average height of Class 9)

n
2
​
=15 (number of students in Class 10)

A
2
​
=154cm (average height of Class 10)

Substitute the values:

Combined Average=
20+15
(20×147)+(15×154)
​

Combined Average=
35
2940+2310
​
=
35
5250
​
=150cm