The average of six numbers is $20$. If one number is removed,the average becomes $15$. What is the number removed?

The average salary of workers in $AMS$ careers is $Rs. 2,000$,the average salary of faculty is $Rs. 4,000$,and the average salary of management trainees is $Rs. 1,250$. The total number of workers could be:

In a school, the average age of students is $6 \, \text{years}$, and the average age of $12$ teachers is $40 \, \text{years}$. If the average age of the combined group of all the teachers and students is $7 \, \text{years}$, then the number of students is?

The average of $11$ numbers is $10.9$. If the average of the first six is $10.5$ and the average of the last six is $11.4$, find the middle (sixth) number.

The average of five consecutive even numbers starting with $4$ is:

The average of certain first consecutive natural numbers is $20.5$. Find their sum.