In a series of $100$ observations, half of them is equal to $p$ and remaining half equal to $-p$ if the standard deviation of these observations is $10$ then $|p|=$__   

Two sets each of $20$ observations, have the same standard deviation $'5'$. The first set has a mean $'17'$ and the second set mean $'22'$ then standard deviation of the combining the given two sets is

Mean, Median and Mode may be the same for some data.

mean deviation from mean of the data