What is standard deviation? How does it differ from mean deviation? What are its advantages and disadvantages?

What is standard deviation? How does it differ from mean deviation? Wh

1.	What is standard deviation? How does it differ from mean deviation? What are its advantages and disadvantages?
Answer» Solution :Standard deviation is the SQUARE ROOT of the arithmetic mean of the squares of all DEVIATIONS. Devations being measured from the arithmetic mean of the items. Merits :- 1. Based on all VALUES. 2. A certain measure. 3. Little effect of a change in sample. 4. Algebraic Treatment. Demerits :- 1. DIFFICULT to calculate. 2. Importance to extreme values.