Class 11 Maths Statistics | Shortcut method |

**Shortcut method for calculating mean deviation about mean**

We take an assumed mean which is in the middle or just close to it in the data. Then deviations of the observations (or mid-points of classes) are taken from the assumed mean. This is nothing but the shifting of origin from zero to the assumed mean on the number line.

If there is a common factor of all the deviations, we divide them by this common factor to further simplify the deviations. These are known as step-deviations

The deviations and step-deviations reduce the size of the observations, so that the

computations viz. multiplication, etc., become simpler. Let, the new variable be denoted by d =(xi –a)/h where ‘a’ is the assumed mean and h is the common factor. Then, the mean x by step-deviation method is given by

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