The mean of the series $a, a + nd, a + 2nd$ is

The arithmetic mean of $n$ observations is $\bar{x}$. If the sum of $n - 4$ observations is $K$,what is the mean of the remaining observations?

If for some $x \in R$,the frequency distribution of the marks obtained by $20$ students in a test is:
Marks: $2, 3, 5, 7$
Frequency: $(x+1)^2, 2x-5, x^2-3x, x$
Then the mean of the marks is:

The central value of the set of observations is called

If the mean of $3, 4, x, 7, 10$ is $6$,then the value of $x$ is

In a class of $100$ students,there are $70$ boys whose average marks in a subject are $75$. If the average marks of the complete class are $72$,then what are the average marks of the girls?