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

For a symmetrical distribution,if ${Q_1} = 25$ and ${Q_3} = 45$,the median is

Let $x_1, x_2, \ldots, x_{11}$ be $11$ distinct positive integers. If we replace the largest of these integers by the median of the other $10$ integers,then:

The mean of $50$ observations is $36$. If two observations $30$ and $42$ are removed,what is the mean of the remaining observations?

Consider a set of observations ${x_1}, {x_2}, {x_3}, ..., {x_{101}}$ such that ${x_1} < {x_2} < {x_3} < ... < {x_{100}} < {x_{101}}$. The mean deviation of this set of observations about a point $k$ is minimum when $k$ equals: