The  average  salary of the entire staff in an department  is Rs. $2000$ per month . The average salary of officers is Rs. $3000$ and that of non-officers is Rs. $1500$. If the number of officers is $10$, then find the number of non-officers in the office?

The average of $\text{'}n\text{'}$ numbers is$z.$ If the number $x$ is replaced by the number  $x^1$, then the average becomes $z^1$. Find the relation between$n, z,$ $z^1$$, x$ and $x^1$.

A person travels three equal distances at a speed $x km/h$ ,$y km/h$,  $z km/h$respectively. What will be the average speed during the whole journey.

Read the following passage and answer the following question that follows.

Aman, Binod, Charan, Dharam and Ehsaan are the members of the same family. Each and everyone loves one another very much. Their birthdays are in different months and on different dates. Aman remembers that his birthday is between $25th$ and $30th$, of Binod it is between $20th$and $25th$, of Charan it is between $10th$and $20th$, of Dharam it is between $5th$ and $10th$ and of Ehsaan it is between $1st$and $5th$ of the month. The sum of the date of birth is defined as the addition of the date and the month, for example $12th$ January will be written as $12/1$ and will add to a sum of the date of $13$. (Between $25th$and $30th$ includes $25$ and $30$).

If the dates of birth, of four of them are prime numbers, then find the maximum average of the sum of their dates of birth?

The average age of a group of person going for a movie is $20$ years. $10$ new person with an average age of $10$ years join the group on the spot due to which the average of the group becomes $18$ years. Find the number of persons initally going for the movie.

An engineering college has only four batches that contain $20,40,60$ and $80$ students respectively. The average pass percentage of these classes are $10\%,20\%,30\%$ and $40\%$respectively. Find the pass percentage of entire college.

Find the average of$f\left(x\right), g\left(x\right), h\left(x\right), d\left(x\right)$ at $x=$$1$.  $f\left(x\right)$is equal to $x^2$$+12$,$g\left(x\right)=$$15$$x^3$$-10$,$h\left(x\right)=\log$$10$$x^2$ and$d\left(x\right)=$$x^2$