I am new to SSRS and trying to create a report using designer. I have survey values given by 5 person in 5 columns and 20 attributes in 20 rows. I created a dataset and trying to find the Standard Deviation for the value across all 5 columns for each row. I need Mean also for that pattern; but i can manage to get by "Sum of values divide by count of values". But Standard deviation is not possible due to complex formula. Any help is much appreciated.

Try writing a code object. STDev is easy to write in VB.NET (which is what you write in a code object).

OTOH you can do in in SQL: