Using shortcut method, find the standard deviation for the data:

${\mathbf{X}}_{\mathbf{i}}$	$10$	$15$	$18$	$20$	$25$
$f_i$	$3$	$2$	$5$	$8$	$2$

 

Using shortcut method, find the mean, variation and standard deviation for the data:

Using shortcut method, find the standard deviation for the data:

Using shortcut method, find the standard deviation for the data:

Using shortcut method, find the standard deviation for the data:

The mean and variance of five observations are $6$ and $4$ respectively. If three of these are $5,7$ and $9$, find the other two observations.