If the variance of the frequency distribution

is 160, then the value of $$c\in N$$ is

The frequency distribution of the age of students in a class of 40 students is given below.

If the mean deviation about the median is 1.25, then $$4x+5y$$ is equal to :

The mean and standard deviation of 20 observations are found to be 10 and 2 , respectively. On rechecking, it was found that an observation by mistake was taken 8 instead of 12. The correct standard deviation is

Let $$\alpha, \beta \in \mathbf{R}$$. Let the mean and the variance of 6 observations $$-3,4,7,-6, \alpha, \beta$$ be 2 and 23, respectively. The mean deviation about the mean of these 6 observations is :