If the average of $6$ consecutive even numbers is $25,$ the difference between the largest and the smallest number is

If the mean of $5$ observations $x, x+2, x+4, x+6$ and $x+8$ is $11,$ then the mean of the last three observations is

The average age of a class of $30$ students and a teacher reduces by $0.5 \, \text{years}$ if we exclude the teacher. If the initial average is $14 \, \text{years}$,find the age of the class teacher in $\text{years}$.

$A, B, C$ and $D$ are four consecutive odd numbers and their average is $42$. What is the product of $B$ and $D$?

The average salary per head of all the workers in a company is $Rs. \,95$. The average salary of $15$ officers is $Rs. \,525$ and the average salary per head of the rest is $Rs. \,85$. Find the total number of workers in the workshop.

The average of $6$ numbers is $20$. If one number is removed, the average becomes $15$. What is the number removed?