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

Which of the following averages is most affected by extreme observations?

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

$A$ student obtains $75\%$,$80\%$,and $85\%$ in three subjects. If the marks of a fourth subject are added,then his average cannot be less than.....$\%$

$A$ school has four sections of chemistry in class $XII$ having $40, 35, 45$ and $42$ students. The mean marks obtained in chemistry test are $50, 60, 55$ and $45$ respectively for the four sections. The overall average of marks per student is: